While the majority of Windows CE users have found ActiveSync (AS3) to be a signficant improvement over CE Services, there are some people who are having difficulty getting it to work. I have captured some of the tips from the microsoft.public.windowsce newsgroup here for the benefit of those who are having problems.
If you upgraded AS3 over CE Services and you are having problems getting AS3 to work try uninstalling AS3. That will not only remove the AS3 files, but should remove CE Services files and registry entries. Reboot and then install AS3.
A troubleshooting tip that worked for CE Services should also work for AS3. If you just can't seem to get synchronization to work after you have already created a partnership try deleting the partnership and then re-creating it. In ActiveSync select File/Delete Partnership. Then connect your device and the partnership wizard should start. To take this even step further, when you create the new partnership you might want to add the synchronization options one at a time to determine which one is causing your problem.
Some people are having difficulty getting ActiveSync to recognize their com port. Windows 9X users might be able to fix this by doing the following.
If you are running Windows NT check to see whether any direct cable connections are set up for RAS. If they are delete them and then try Get Connected. Better yet, if you weren't using RAS for anything other than CE Services you can delete it all together by opening Network Properties, selecting Remote Access Service and clicking on Delete.
People who have Windows CE software that synchronizes with the desktop using ActiveSync have been getting the following error message: "Unable to find ActiveSync manager..." An example of a program that experiences this is HPC Notes. Microsoft has written a patch for this problem which you can download from Phatware's web site. If you aren't using ActiveSync Version 3 you will not need this patch.