When using the N900, one of the annoying thing I regularly get is the ActiveSync error. There are message about error connecting to the server or something like that, but on observation the mail and calendar is already synchronized. Contacts in the other hand… too much to check.
Anyway, it’s just me, but the error notification in the notification area is like a sore thumb and it won’t disappear until a successful synchronization is made, which could be god knows when.
Until lately, I could synchronized just the mail part from the mail application and it usually succeed (which probably means either I had too much data, or something with the contacts). When this one succeed, the notification is gone.
This doesn’t actually fix the real problem though. I think I read somewhere that having merged or duplicated contact in some way in the device could contribute to such synchronization errors.