Salutations, I would love to help but I'm gonna need a little more info. :)
What version of Palm desktop are you using?
What platform?
Are you going through serial/USB/Serial-to-USB converter?
What OS are you using?
Are you going through a cradle or a sync cable?
Have you tried different hardware?
The only thing I can think of offhand is to try backup buddy. See if that works. if that backs up everything then you may have a software problem. If it doesn't then you may have a hardware problem. Try lowering the serial speed.
Good luck,
David