During VMware backups, encountering the error message "Unable to retrieve queryChangedDiskAreas even after CBT query retry" indicates a failure to track Changed Blocks of a virtual machine (VM) within BDRShield.

The error may arise due to various scenarios:

1. If an external application interferes with VM's Changed Block Tracking (CBT), it may disrupt the tracking key managed by BDRShield, leading to a failed retrieval of CBT data.

2. If an external application alters the CBT status of a VM (disabling and re-enabling), CBT data may become inaccessible for that VM.

To address this issue, follow these steps:

1. If CBT is disabled, enable it using these steps:

1. Power off the VM.
2. Right-click the VM, select "Edit settings," navigate to the "Options" tab, and click "Configuration Parameters."
3. Set "ctkEnabled" value to "False."
4. Set "scsi0:x.ctkEnabled" value to "False" for each disk of the VM in question.
5. Remove any -CTK.VMDK files from the source folder.
6. Power on the VM.
7. Power off and power on the VM again to update the CTK table.
8. Rerun the Backup job.

2. If the backup job involves a single VM, perform an additional full backup after following the above steps.

3. If the backup job involves multiple VMs and all are affected by the same issue, consider running an additional full backup.

Note:

1. Running an extra full backup is not recommended when only a subset of VMs within a multi-VM backup job faces this issue. Instead, opt for incremental backup.
2. Avoid using third-party applications on the same VM intended for backup with Vembu.