When you get this error you should see the following event in the event viewer on the Exchange server.
Event ID: 1008
Source: MSExchange ActiveSync
An exception occurred and was handled by Exchange ActiveSync. This may have been caused by an outdated or corrupted Exchange ActiveSync device partnership. This can occur if a user tries to modify the same item from multiple computers. If this is the case, Exchange ActiveSync will re-create the partnership with the device. Items will be updated at the next synchronization.
Make sure the user who is trying to connect with his phone has the option ‘Include inheritable permissions…’ checked on.
(Active directory -> right click the user -> properties -> security -> advanced -> ‘Include inheritable…’).
Note: If you don’t see the option ‘Security’ go to Active directory -> view menu -> check ‘Advanced Features’.