Failed to determine disk areas to backup for VM disk (4044325)

Netvault Vmware Plugin Backup fails with the following error:

"Failed to determine disk areas to backup for VM disk"

The sub context reveals that it is not possible to locate the changed block.

VMWUTIL :03188 6 0 91237 LoginToServer success=TRUE
VMWVIM :03188 686 0 91238 Failed to get changed disk areas: 12

VMware have identified some cases, such as a power failure or hard shutdown while virtual machines are powered on, where CBT might reset and lose track of incremental changes. Likewise offline Storage vMotion, but not online Storage vMotion, could reset but not disable CBT.

More information can be found in VMware Knowledgebase article 1020128 "Changed Block Tracking (CBT) on virtual machines"

http://kb.vmware.com/kb/1020128

If CBT (change block tracking) is not used in the Backup Options tab of such backup, the job will succeed. However if CBT is desired then the following must be done before a successful backup can be taken:

a) Turn off the VM

b) Disable CBT
Edit the .vmx file of the virtual machine. Use vi or your favourite editor

Before editing it will look like this:
scsi0:0.ctkEnabled = "TRUE"
ctkEnabled = "TRUE"
 

After edting :
scsi0:0.ctkEnabled = "FALSE"
ctkEnabled = "FALSE

c) Stun/unstun cycle (Turn VM power on then off)

d) Enable CBT
Edit the .vmx file of the virtual machine. Use vi or your favourite editor

Before editing
scsi0:0.ctkEnabled = "FLASE
ctkEnabled = "FALSE

After edting:
scsi0:0.ctkEnabled = "TRUE"
ctkEnabled = "TRUE"

e) Stun/unstun cycle  (Turn VM power on then off)

f) Run the full backup job with CBT option selected (in the Backup Options tab).