I am having Sync problems, too. It worked fine until yesterday. I am now getting this message:
"Synchronization cannot be completed successfully. Reconnect your device and try again. If the problem persists, see the Microsoft... blah blah blah..."
It DOES connect. I can explore the device, move files, etc. Just no sync. Very strange.
I was using 4.1 (came on the disc with the X51v I got last week). Upgraded to 4.2 from the web. No luck. Uninstalled. Installed 4.5 beta. No luck. Tried just about all the advice in this thread and in the trouble shooter.
All I am using for virus protection is AVG free edition.
The only cause for this that I can think of is found in this thread:
http://www.aximsite.com/boards/showthread.php?t=140677
I was getting an error message, then I re-installed PocketInformant. The error message is gone, but now no sync.
Any guesses?