After an backup has been applied any license on the Switchvox must be registered again. Until this is done you will see an ERR.
You can use the same license key to register the license.
To re-register a license:
Log into the admin portal of the Switchvox
Go to Tools>Digium Add-on Products
Select the product that you are trying to register and enter the License Key
Select "Register Product"
If you receive an error contact support to make sure the license has valid registration attempts.