2008 Server - VSS Errors

We have Windows Server 2008 Standard SP2 running VSS on 3 drives, D, E and F.
It's a file server and locks up and is only solved with a reboot.
The VSS runs 3 times a day and are hours apart in schedule and there is plenty of space available on the drives.
Event viewer shows these 3 VSS errors below:

1. The flush and hold writes operation on volume F: timed out while waiting for a release writes command.

2. Volume Shadow Copy Error: VSS waited more than 40 seconds for all voumes to be flushed.  This caused volume \\?\Volume{47c28d67-4ae3-11de-865d-0014220d1366}\ to timeout while waiting for the release-writes phase of shadow copy creation.  Trying again when disk activity is lower may  solve this problem.

Operation:
   Executing Asynchronous Operation

Context:
   Current State: flush-and-hold writes
   Volume Name: \\?\Volume{47c28d67-4ae3-11de-865d-0014220d1366}\

3. Volume Shadow Copy Service error: The I/O writes cannot be held during the shadow copy creation period on volume \\?\Volume{47c28d67-4ae3-11de-865d-0014220d1366}\. The volume index in the shadow copy set is 0. Error details: Open[0x00000000], Flush[0x00000000], Release[0x00000000], OnRun[0x80042314].

Operation:
   Executing Asynchronous Operation

Context:
   Current State: DoSnapshotSet


We have also Symantec Backup Exec running on another server that is backuping up these drives, but NOT during the VSS Snapshots.

Any help? Thanks!