Avamar - Exchange Backups failing with Backup Agent is not running under Avamar Backup user account

Avamar Exchange Backup failing with "avexvss Error <18187>: Backup Agent is not running under the Avamar backup user account".
Backups fail even after the AvamarBackupUser is part of all the required groups.


2019/03/29-08:16:52.16300 [avbackupusercfg.exe]  CN=AvamarBackupUser,CN=Users,DC=#######,DC=se
2019/03/29-08:16:52.16300 [avbackupusercfg.exe]  Leaving function -createuser::GetSearchStrLDAP
2019/03/29-08:16:52.17899 [avbackupusercfg.exe]  User is member of CN=Avamar Roles group
2019/03/29-08:16:52.17899 [avbackupusercfg.exe]  User is member of CN=Organization Management group
2019/03/29-08:16:52.17899 [avbackupusercfg.exe]  User is member of CN=exchange.trusted subsystem group
2019/03/29-08:16:52.17899 [avbackupusercfg.exe]  User is member of CN=exchange.servers group
2019/03/29-08:16:52.17899 [avbackupusercfg.exe]  User AvamarBackupUser is NOT a member of Exchange Servers group

In the above scenario, even if the security group memberships are correctly assigned, the group naming convention is an Exchange Legacy Distinguished Name different from the Default security group names.

Example: 
2019/03/29-08:16:52.17899 [avbackupusercfg.exe]  User is member of CN=exchange.servers group
2019/03/29-08:16:52.17899 [avbackupusercfg.exe]  User AvamarBackupUser is NOT a member of Exchange Servers group

Ensure that the required permission/memberships have been provided to the "Avamarbackupuser" 

Please refer to the documentation on the Avamar Plug-in for Exchange VSS product page.

If you have an Exchange Legacy Distinguished Name for the AvamarBackupUser account.