After upgrading to 5.5 a COS quiesced backup of Windows 2008 64 bit VM's that resides on an ESX 4.1 host fail with
Error Message: Application-quiescing is not supported on Windows 2008 virtual machine backups (Failover to COS)."
Before the upgrade the backups were successful.
When the ESX Console job runs, it changes the Disk Enable UUID value to TRUE.
As a work around you can backup these failing VM's via VA.
There are two options
1) VA- SAN (this will require Enterprise licensing as a minimum)
2) VA-LAN
Please refer to the following video link on deploying the VA and using it for backup.
https://support.quest.com/SolutionDetail.aspx?id=SOL93538
Waiting for fix in a future release of vRanger.