Cannot assign encryption key to multiple jobs.

Following a migration to new hardware and a new OS, we can no longer assign an encryption key to the jobs.

Only one user account configured on server: System logon account

Only one encryption key configured on server, this key was configured today (18th), over two weeks since the migration: Created by: System logon account - Restricted: Yes

When trying to assign this key to jobs, an error is encountered:

"Unable to save the backup (job name). The restricted encryption key '%1' cannot be used because the key owner cannot be validated. Verify that the user account for the key owner exists and is not disabled or locked out, or choose a different encryption key.

Calling Method 'UpdateBackup'
BEMSDK Method 'CBemPolicy.Update'
BEMSDK Failure Code: E0008850
Error: -536836016:The restricted encryption key '<key name>' cannot be used because the key owner cannot be validated. Verify that the user account for the key owner exists and is not disabled or locked out, or choose a different encryption key."

We have the same encryption key and system logon account configured on our other backup server and this is working without a problem.