I ran across this problem not too long ago where after upgrading to a new file server, users that had been previously synchronizing their Offline Files were having issues with Offline Files still trying to synchronize with the original / old file server name.   The old server was already decommissioned and removed, so the only way I could resolve this was by doing the following steps in order:

-Disabling Offline Files
-Restart the PC
-Delete the C:\Windows\CDC directory
-Delete registry key:  HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\NetCache
-Restart the PC
-Enable Offline Files
-Restart the PC