Backup fails if you enabled Changed Block Tracking for virtual machines

Backups might fail if you enabled Changed Block Tracking (CBT) for virtual machines. 

The log files are created at /var/log/Phoenix. 

Resolution

1. Login to the backup proxy.

2. Disable the CBT of virtual machine using vmcontrol utility.

3. Enable the CBT of virtual machine using vmcontrol utility.

Note: This utility deletes all the snapshots in the virtual machine.