Maybe coincidence and maybe not. I think the trial version of PlanPlus killed my Palm's ability to synch my date book. Even after removing it (I think I removed it, but maybe parts remain) from both the handheld and the desktop, I can't get this function to work now. I have a Zire 71, granted it is 3 years old but it has been problem free and never been dropped or zapped, and there is a lot of memory left in it.
Any suggested methods of resusitation?