Has this happened since upgrading to Service Pack 12 by any chance?
Had exactly the same issue, turns out the VMDK clients were always getting an error, but a change in Service Pack 12 meant that unable to quiesce the guest file system during the initial snapshot would result in an error being generated, despite the second crash consistent snapshot working okay
Looking at the Event Viewer in Windows helped us further and most of the clients had VSS errors, that I have passed on to my Windows team
I was told the danger is if you are using the 'Quiesce Guest File System' on database servers such as SQL, Exchange, in our case we use the appropriate Commvault agent
We were given the Additional Settings parameter 'ignoreQuiesceGuestErrors' set to 1 and these errors were no longer reported, but we were happy with the risks involved as all databases use agents or are dumped to disk
Hope this helps