I couldn't sync my iPhone to MacBook Pro.  iTunes kept saying "syncing has been disabled on this computer".

Here's a quick fix:

In the Finder find the directory Library : Application Support : SyncServices

Rename the folder SyncServices to something like temp_SyncServices.  Restart your compute, connect your iPhone and it should sync.

Related link:

http://discussions.apple.com/thread.jspa?threadID=1122225&tstart=0