The error they were experiencing was:
User synchronization failed. Update abandoned
After speaking to Symantec this issue can occur sometimes with Schemus due to corruption in one of the following files:
In our case it was:
To fix this problem, first close Schemus.
Next rename or move these files to another location.
Lastly reopen Schemus and attempt another sync, these files will regenerate. After making this change Synchronisation is now working correctly.