Switchvox - Why do I see the error: RESFAX ERR ERR on Sangoma Addon Products page?

Faxes are not working and the Sangoma Addon On Products page (go to Tools > Sangoma Addon Products) shows the following:
RESFAX ERR ERR [FAX-XXXXXXXXXXXXP Date Time]

This usually happens after restoring the server from a backup. The Sangoma Addon Products (such as a Fax License) will need to be re-registered.

You will need your full registration code. If you are not sure what it is, please call Technical Support to obtain it.
Once you have your Full Registration Code go to this link Why am I unable to register more than one fax license? and follow the instructions to re-register your fax license.

Please note that a software restart is sometimes required for the new fax software to run correctly.