When performing full backups with CBT enabled, the CBT operation may fail with error "Change Block Tracking not enabled on <disk>". When performing incremental or differential backups of the same VMs, CBT will function properly.
The following scenarios hav been shown to cause this error, although not in all cases:
In some cases, performing the following operation has resolved this issue.
In some cases, deleting the *.ctk.vmdk file for each disk in the affected VM has been shown to resolve this issue.