I had the same problem as you describe, After many unsucessful attempts to get active sync to work, I began at the begining and reinstalled the operating system to my laptop [with full format of the c drive] and active sync( and all is ok with the world) ( xp sp 1 to my dell c400)-

yes I also forgot to take a backup of the X5 so the job of recreating all the data begins lol
BUT THE X5 WORKS !!!!!