Let's recap what has been written about the so called "Ita Mandara" (Board Mandala) or "dai- gohonzon" of Taisekiji........much of this has appeared over the last  year on the internet, but, for the sake of new people, here it is again:
 
  1.   Board mandalas first appeared int the later Muromachi
  Period (post 1333 AD), long after Nichiren's death.  These
  board mandalas were associated with Hokke fraternities and
  Hokke Halls that sprang up in the Muromachi period.    The
  term "Hokke Shu" ( or Hokke Ko, which is "Lotus Sutra
  confraternity), which is written on the so-called
  dai-gohonzon, was not used during Nichiren's lifetime but
  several decades later.  In fact, the Tendai sect took the
  Nichiren temples to court over the use of the term, "Hokke
  Shu", which, up till the Muromachi period, was used
  exclusively by the Tendai sect.  The Tendai sect regarded
  the Nichiren movement as just an offshoot of the legitimate
  Tendai sect, and therefore exerted its right to the use of
  the name, "Hokke Shu" (Lotus Sect).  This tell tale
  discrepancy of the term "Hokke Shu" (or Hokke Ko) places the
  date of the so-called "dai-gohonzon" well beyond its
  supposed date of 1279.
 
  2.  The so-called "dai gohonzon" is inscribed on camphor
  wood which does not grow on Minobusan.  Camphor wood
  ("kusunoki") is only found along the coast in southern
  Kyushu (the coastline running along the Japan current or
  "Kuroshio").  It was (and still is) astronomically
  expensive; therefore, if it were a donation from a believer,
  there would have to be a reliable historical source to
  authenticate its improbable existence on a mountain, far
  from the tropical coastline.  There is no such historical
  source at all.
 
  3.  Taisekiji claims that the so-called "dai gohonzon' was
  carved by Nippo on Mt. Shichimen ( an neighboring mountain
  to Mt. Minobu).  But Shichimenzan had no part in the life of
  Nichiren, and did not belong to the lands that Lord Hakiri
  controlled, hence was off limits to Nichiren and his
  disciples.  Lord Hakiri was the landlord of Mt. Minobu and
  he sheltered Nichiren there for the last 9 years of his
  life.  Nippo was a well known sculptor, as well as a
  disciple of Nichiren, but he never worked at Minobusan or
  Shichimenzan.
 
  4.  Nikko never mentions this so-called "dai gohonzon" in
  any of his authenticated writings.  The first mention of the
  details about the so-called "dai gohonzon" was recorded in
  the "Kechu Sho" which dates from 1662.  Even there, the
  reference has been tampered with.  There are no reliable
  historical documents that mention the so-called "dai
  gohonzon".  Nichiren never mentions it, Nikko never mentions
  it.  The first word of it is in 1488, when Nichi-u announces
  it to the world.  This "ita mandara" was attacked by
  Nichijo, head priest of Kitayama Hommonji, a contemporary of
  Nichi-u.  Nichijo reports that Nichi-u had become a leper, a
  severe retribution for "having gone against the fundamental
  intention of the founder of the temple, and the carving the
  ita mandara, which had never been seen or heard of; he also
  produced forged books adorned with his own doctrines" (from
  the "Taisekiji Kyowaku Kempon Sho" or "The Insane Revelation
  of the Original Buddha at Taisekiji", written by Nichijo.)
  Note that Nikko spent the last 36 years of his life at this
  Kitayamam Hommonji and his grave (which faces Minobusan, not
  Taisekiji) is there.  This Hommonji was probably the best
  candidate for the "Hommonji" that is mentioned in the forged
  "transfer documents".  The name, "Taisekiji" cannot be
  mistaken for "Hommonji". Nikko left four authentic mandalas
  by Nichiren at Kitayama Hommonji.  He added, in his own
  handwriting, the following inscriptions , "Hanging it up in
  the Hommonji, one should make it the esteemed jewel of the
  Latter Age".  Each of these four mandalas has such an
  inscription from Nikko.  These mandalas ended up at several
  other Nikko temples, but the reference to "Hommonji" at
  Kitayama is irrefutable.  Of the eight Nikko temples, four
  received authentic Nichiren gohonzons.  Taisekiji did not
  receive such a prize from Nikko at all.  Nikko never
  mentions a supreme board mandala.  If he left this supreme
  treasure at Taisekiji, then he NEVER again returned to
  Taisekiji to see it, nor did he orient his grave toward it.
  His instructions regarding his grave, in his own
  handwriting, is that it face Minobusan.  This would be an
  unthinkable breech of etiquette if a "supreme dai- gohonzon"
  was left at Taisekiji.  Nikko left Taisekiji after only 18
  months there, and he spent the rest of life at Kitayama
  Hommonji, never returning to Taisekiji again.
 
  5.  Insofar as can be ascertained from the one circulated
  photograph of the so-called "dai- gohonzon" (taken in 1910,
  with permission of Taisekiji), the handwriting is VERY
  peculiar.  Nichiren's handwriting has been carefully studied
  and catalogued by the late Suzuki Ichiro and Yamanaka
  Kihachi.  The handwriting of the so-called "dai gohonzon" is
  from the 3rd year of Koan (1280), not the 2nd year of Koan
  (1279), which is the formal date on the "ita mandara".  It
  is almost a carbon copy of a genuine Nichiren gohonzon of
  1280, now at Myokaiji in Numatsu near Fuji.  It is important
  to note that the SGI/NST gohonzons, inscribed by various
  high priests of Taisekiji, are VERY different, both in form
  and content, from the so-called "dai-gohonzon".  Certain
  placement of kanji have been conspicuously altered, and
  phrases has been added to the body of the honzon.  Such
  phrases never appeared in any other Nichiren gohonzon, and
  are incongruous with the nature of the gohonzon.   (These
  are the phrases referring to "gain" and "loss", on either
  side of the SGI/NST honzons).  The SGI/NST honzons claim to
  be faithful copies of the so-called "dai-gohonzon" but they
  are very different from the prototype, especially with
  regard to the size of the kanji in Nichiren name and his
  "kao" ("flower stamp").  In general, the size of the Daimoku
  is larger than that found on Mandalas written in 1279 and
  before then.  This size of Daimoku was found on gohonzons
  from 1280, 1281 and 1282.  So, the so-called "dai-gohonzon"
  is only consistent with gohonzons from 1280 and beyond.
 
  6.  The so-called "dai gohonzon" is conferred upon a
  "Yashiro Kunishige", whose name is completely unknown to
  anyone, either in Nichiren's time or thereafter.  The
  Nichiren Sho Shu High Priest, Hori Nikkyo, who was the
  greatest NST scholar of this century, said, "I do not know
  the basis for this matter of Yashiro Kunishige" (Source:
  Fuji Shugaku Yoshu, published by NST itself).  Hori Nikkyo
  could not come up with any historical source for Yashiro
  Kunishige.  It could not stand in for the farmers of the
  Atsuhara persecution because peasant farmers did not have
  last names in those days.   Over half of all of Nichiren's
  authenticated mandalas do not bear personal inscriptions on
  them.  Hence, the argument that they were designated for
  personal use and not "for all mankind" cannot be supported.
  The term "ichienbudai' is the Japanese rendering for
  "Jambudvipa".  The translation, "for all mankind" is really
  a stretch for the classical Buddhist name of Jambudvipa (the
  southern continent of a Mt. Sumeru system).
 
  7.  Neither Nikko nor Nichiren ever inscribed gohonzons on a
  plank of wood.  Nikko specifically forbade the transferring
  of a gohonzon from paper to wood, in his own writing,
  "Fuji-isseki- monto-zonji-no-koto", claiming that an
  engraving on a plank would belittle the value of the
  original handwriting.  This was written in response to the
  request of several believers to create a wooden mandala,
  which was just then being introduced for the first time
  (1333, the same year that Nikko died).  Because of so many
  fires, temples were seeking ways to preserve their paper
  treasures by transferring them to wood.  Nikko was adamantly
  opposed to any such transfers from paper to wood and scolded
  the believers for suggesting such a thing.
 
  8.  Nichi-u claimed that the so-called "Ita Mandara" was the
  most legitimate gohonzon that Nichiren intended to inscribe,
  and that all other mandalas written by Nichiren were
  "worthless".  The copying of a gohonzon is not a prohibited
  practice, but the claim that the imitation "ita mandara" was
  the only "genuine or supreme" mandala is where the blasphemy
  occurs.  It is not correct to dismiss all other authentic
  Nichiren gohonzons with the shaky claim that there is one
  "supreme mandala".  Only a statement to that effect from
  Nichiren himself could be trusted. And Nichiren never makes
  any mention of a "supreme mandala" in the form of a "ita
  mandara".  ALL gohonzons, according to Nichiren, are the
  SUPREME mandalas.  ("dai-mandara' is used by Nichiren to
  describe all of his gohonzons.)  The only claims from
  Taisekiji are obvious forgeries, which date from the 15th
  century.  No other copies of any substantiating documents
  exist outside of the walls of Taisekiji itself.
 
  The history of succession at Taisekiji is replete with cases
  of leprosy, palsy, madness, cancer of the mouth and throat,
  etc.  These are serious retribution for slander, evident in
  the lifetime of the particular high priest in question.  In
  truth, the "succession" was never authentic from the start,
  and the "line" has been broken over a dozen times.  High
  priests have taken Taisekiji to court in the past, they have
  deserted their high office, never to be heard from again,
  and they have died without naming any successor at all in at
  least six instances.  Three high priest were only children
  at the time of their "succession", one high priest was sued
  in court for having illicit sexual intercourse with his own
  daughter (the case was hushed up in an out-of-court
  settlement).  The stories go on and on, but who cares?  The
  legitimacy of Nichiren's philosophy can only be found in
  Nichiren's own authenticated words, not in the words of
  later priest and not in the words of later forgeries.  There
  is no mention of a so-called "ita mandara" in Nichiren's own
  lifetime.  Nichiren's hut at Minobusan was only 10 square
  feet.  There was no place to put such a board mandala in his
  small hermitage.  (The temple, Kuonji was not built at
  Minobusan until 1281.)  How could it have been kept secret
  if there was no place to conceal it?
 
  1419   Nichiei, the 8th High Priest, unable  to  find  a
  successor, transfers  the  heritage  of  the Law to Aburano
  Joren, a lay believer. This is in the records of
  transmission of Taisekiji itself. (Fuji Shugaku Yoshu, v. 5,
  p.255, "Biography of Nichi-e")
 
  **Mr. Joren transfers it to Nichiu  who  was  only 18 years
  old at the time.
 
  1409-1482 Nichiu, the 9th High Priest, restores the Head
  Temple  which  had  previously fallen into decline as the
  result of the land dispute begun by Nichigo after
  Nichimoku's  death.
 
  Nichijo, the  10th  High  Priest,  and  Nittei,  the 11th
  High Priest, passed away without naming successors so Nichiu
  had to assume office again from 1472 until his death in
  1482.
 
  Nichi-u, the 9th High Priest of Taisekiji, died of
  leprosy....
 
  Several people have asked for some source references for
  this story. The idea that a farmer from Fuji started the
  rumor is not a documented source (and it sounds fishy,
  too...)
 
  The source for the leprosy story is, of all things, from
  Nichiren Shoshu itself!
 
  From the "Fuji-Shuo Gaku Yoo Shuo" (Fuji School of Studies
  V.5 p.39) edited by Horii Nikkyo himself (the greatest
  scholar of Taisekiji of this century and a High Priest,
  retired)...it says:
 
  "The 9th generation of Taisekiji, Nichi-u, became a leper."
 
  And again in Vol.7, p.44 of the above mentioned edition by
  Horii Nikkyo, there is an attack against Nichi-u for various
  transgressions.  In  the "Koomom Shoo-gi", p.211 (Orthodoxy
  of the Nikko  School) another reference to Nichi-u and his
  leprosy is made
 
  One would ask why Horii Nikkyo would attack one of his
  predecessors. The answer I got is that he was an honest
  scholar and printed many things that were historically
  accurate but not popular with Taisekiji. (He was, after all,
  a former High Priest, and no one was about to criticize him)
    It was Horii Nikkyo who said that he had no idea who
  "Yashiro Kunishige" (the name on the dai-gohonzon) was, or
  which story of how the mandala came into Taisekiji's
  possession is true. Nichi-u himself said that Kunishige
  transferred it to Taisekiji in the 15th Century, which
  contradicts the story that he had it transferred to wood
  from a paper gohonzon that had been "hidden" for two hundred
  years.  The popular version today is that the wooden mandala
  was taken by Nikko from Minobusan to Taisekiji, but there is
  no mention of such a large wooden mandala being brought to
  Taisekiji.  After all, it couldn't be concealed in someone's
  sleeve and it is a heavy, obvious object.
 
  1482   Nitchin becomes appointed the 12th High Priest at 14
  years of age  by  Nichiu  (before  Nichiu's death).
 
  Nitchin at some point later in his life  then  transfers
  the office  and heritage of the Law to Nichiin, a 10 year
  old boy  who, though considered High Priest at that age,
  didn't  even            begin  his  study  of  the
  Daishonin's Buddhism till 3 years later after he became 13.
 
  At some point in the mid to late fifteen hundreds
  Taiseki-ji began to fall into serious decline.  The main
  reason for this was because it was located far away from
  the  political  and cultural  center  of  Kyoto.   As  a
  result,  the priests at Taiseki-ji started the process of
  importing  candidates  for High  Priest  from  the  Yoho-ji
  temple, a branch sect of the Nikko school, in Kyoto. The
  Yoho-ji  temple  held  doctrines that   varied
  significantly   from  the  orthodoxy  of  the Daishonin's
  Buddhism.  In particular, they considered Shakyamuni to be
  the True Buddha (as opposed to Heretical Taisekiji) and used
  his statue as an appropriate object of worship.  The first
  such candidate to assume the role of High Priest, Nissho,
  was invited in 1594 by the 14th High Priest Nisshu. This
  reign of High Priests imported from Yoho-ji  temple
  continued for  almost  a hundred years until 1692 when
  Nikkei, the 23rd High Priest, passed away.
 
  1596   Nissho, the 15th High Priest, erects a statue  of
  Shakyamuni as the object of worship and encourages the
  recitation of the entire 28 chapter Lotus Sutra as practice.
 
  Nissei, the 17th High Priest (who  was  ordained  at
  Yoho-ji temple)   writes   the,  "Chronological Accounts  of
   Sage   Nichiren," encouraging believers to worship a statue
  of Shak   yamuni and to recite the entire Lotus Sutra.
 
  In a  dispute  with  Kyodai'in,  the  great-granddaughter
  of Tokugawa  Ieyasu  and an influential lay patron who built
  the Miei-do temple in 1632, Nissei quit the office of High
  Priest and left the head temple leaving no successor.
 
  1641   Nisshun, the 19th High Priest, went to Jozai-ji
  temple to  be  recognized  as legitimate successor by Nissei
  after receiving  authorization from the  shogunate
  government  for  the  head temple's  domain.   Nissei  made
  peace  with  Kyodai'in (see  above) and returned to the head
  temple to officially  appoint Nisshun to be the 19th High
  Priest in 1645.
 
  1718   Nichikan Shonin, a parasite, becomes the 26th High
  Priest and destroys the teaching of Nichiren, Nikko,
  Nichimoku, etc..   He wrote tirelessly to distort the
  Daishonin's  teachings,  including the  Rokkan  Sho  (lit.,
  "Six-Volume Writing") which is one of the most bizarre
  pieces of Buddhist literature ever written, with  the
  incorrect interpretations of the Daishonin's teachings.
 
  In short, the light of common sense and logic do not support even the
  smallest shred of evidence for a so-called "dai-gohonzon" in the lifetime of
  Nichiren.  Nor even in the lifetime of Nikko. They do not  have not shed not
  one drop of evidence to support the Taisekiji- SGI theology, **NONE**.