The virtual machine may be too busy to quiesce to take the snapshot.

Hello,

Got this issue:

Note: Resource: "VM xx" is not snappable. Attempting to back up directly from the source volume.
V-79-57344-38260 - Unable to create a snapshot of the virtual machine. The virtual machine may be too busy to quiesce to take the snapshot.

My enviorment:
BE 2012 sp3 hotfix 1, ESXi 5.5xx via Vcenter
VM OS 2008 / Just 1 50gb thin vmdk 

Tried following troubleshooting:

-updated VMtools, BE cleint -reboot
-manually able to create and delete snapshot just fine
-no old left over snapshots
-created new job
-same issue with GRT /non GRT
-account used is full admin, backups for other VM's working fine
-backup via remote agent works
-aofo option is selected

Any further suggestions?

Thanks in Advance