I keep getting this error message when syncing my iPhone. Why?

When I seek to sync my iPhone, I get this message:

"iTunes cannot sync information with the iPhone “Russell Swaim’s iPhone” because syncing has been disabled on this computer. Do you want to enable syncing?"

I hit "yes" togive permission to sync, but in the next box i get this message: "Syncing cannot be enabled in this computer."

Soooo... I press the "Override" button. But it still doesn't sync.

Any help?

Thanks,

Russ