Unable to access file [unspecified filename] since it is locked

VMware holds a lock on the snapshot file while it is being consolidated. If there is an issue during this process, it is possible for further snapshots to be unable to consolidate, causing removal failures. You receive warnings that the snapshot removal process failed because '<unspecified filename>' is locked. Specifically:

RemoveSnapshot failed, snapshotRef "snapshot-xxx", timeout "3600000"
Unable to access file <unspecified filename> since it is locked

There are two possible causes:

1. The VMware host held a lock on that snapshot, typically due to a communication error between Veeam and the host/VC.
2. Virtual Appliance mode failed to unmount hot-added disks, which prevents the snapshot from being commited.

1. If the VMware host held a lock on that snapshot
2. Restart the management agents on that host
3. Create a snapshot manually
4. Perform a "Delete All" operation. Note: This may cause a temporary "stun" period, so take necessary maintenance precautions if necessary. IE http://www.veeam.com/kb1681
5. This should clear the snapshot(s) present

1. Remove all hot-added disks from the Veeam VM
2. Create one snapshot manually
3. Perform a "Delete All" operation

If the first problem occurs frequently, it is worth checking both the network connection between Veeam and the source host, as well as the overall load on the source host at the time the backup typically finishes.