My Treo 650 quit syncing calendar events a while back. It would reliably generate an "AirSAMStateMachine.c" error.

I found the secret decoder ring for these messages. "1509" means "Sync interface: Sync protocol has encountered an error. It is usually followed by status code to indicate its particular definition." Sure enough, it's followed by "Status: 5", which means, simply, "Server error.".

The Exchange server wass not logging an error, though. Nothing in the event log. Nothing in the IIS log. I applied the standard exchange ritual voodoo: checked information store for errors using eseutil, etc; ensured IIS was bound to all IP addresses (the server is multihomed), verified Exchange 2003 SP2 was installed, ensured "basic" and "integrated" auth were enabled and that SSL was not required. Nothing helped.

But I did, in the end, get my Palm syncing again. I simply deleted the mail account on the Treo and re-created it. Apparently the "server error" was really an internal Versamail error.