Server Farm Backup Failing on 2012

Hi

Last few backup jobs on the server farm have failed.  The history says its a logon error but when I attempt to edit the job it says that "The specified machine is not a sharepoint server".

"Final error: 0xe0009b61 - Backup Exec could not log on to the server with the logon account specified for it. The logon account does not have valid credentials. Ensure that the user name and password are correct in the logon account."

This is running on a SBS2011 machine.  Everything was fine for months and as far as i know no changes have been made.

The main backup is running fine and uses the same account.

Not sure if i should be looking at this from a user account of sharepoint angle.

Thanks

G