It means that there is one or multiple calendar entries that cannot b
syncronized with your handheld.  There are multiple reasons

First, there is a know issue with old ActiveSync versions, you shoul
try to upgrade to version 3.8 now available

If the problem remains, it is likely to be caused by an old schedule
recurrent meeting that has been recently updated.  To correct th
problem, you might want to increase the calendar syncronizatio
window to all (ActiveSync calendar settings).  This will allo
ActiveSync to "realize" that the meeting is the same as previousl
scheduled and change is not an error

Worst case scenario, version 3.8 tells identifies the culprit, so yo
can go ahead and fix the item