Hmm..same problem here with
[Mar 12 14:06:01.919] [ debug] [vmbackup] *** VmBackupStart
[Mar 12 14:06:01.919] [ debug] [vmbackup] Using quiesceApps = 1, quiesceFS = 1, allowHWProvider = 1,execScripts = 1, scriptArg = , timeout = 0
[Mar 12 14:06:01.919] [ debug] [vmbackup] Quiescing volumes: 6000c293-c0b9-7b5d-81e0-56433a588686
[Mar 12 14:06:01.919] [ debug] [vmbackup] *** VmBackup_SendEvent
[Mar 12 14:06:01.919] [ debug] [vmbackup] *** VmBackupStartScripts
[Mar 12 14:06:01.919] [ debug] [vmbackup] Trying to run scripts from /etc/vmware-tools/backupScripts.d
[Mar 12 14:06:02.918] [ debug] [vmbackup] *** VmBackupAsyncCallback
[Mar 12 14:06:02.919] [ debug] [vmbackup] VmBackupAsyncCallback: checking VmBackupOnFreeze
[Mar 12 14:06:02.919] [ debug] [vmbackup] Async request 'VmBackupOnFreeze' completed
[Mar 12 14:06:02.919] [ debug] [vmbackup] *** VmBackupEnableSync
[Mar 12 14:06:02.919] [ info] [guestinfo] Poll loop disabled.
[Mar 12 14:06:02.919] [ debug] [vmbackup] *** VmBackupSyncDriverStart
[Mar 12 14:06:02.919] [ debug] [vmsvc] SyncDriver: Freezing using Linux ioctls...
[Mar 12 14:06:02.919] [ debug] [vmsvc] SyncDriver: failed to open '6000c293-c0b9-7b5d-81e0-56433a588686': 2 (No such file or directory)
[Mar 12 14:06:02.919] [ warning] [vmbackup] Error freezing filesystems.
I dont know what
[Mar 12 14:06:01.919] [ debug] [vmbackup] Quiescing volumes: 6000c293-c0b9-7b5d-81e0-56433a588686
means..it is not the uuid of the volume 
Server is a Red Hat Enterprise Linux Server release 5.7