When trying to transfer the Operations Master FMSO role, you get this error:
The transfer of the operations master role cannot be performed because:
The requested FSMO operation failed. The current FSMO holder could not be contacted.
This is could be due to a network routing issue, firewall (local or network) or something else. If you are no longer using the server as a Domain Controller, then you could consider just seizing the role instead of transferring it.