# Revision history [back]

The error "The Session Is Not Authenticated" usually occurs when the VMware Esxi server is having trouble getting change block tracking to work correctly on some of the disks because CBT failed to identify the changed data blocks. A workaround does exist for the issue and this issue can be fixed by following the steps below.

## The following steps will reset CBT on the guest VM and should resolve the issue:

• Power off the VM
• Right click the VM, click “Edit settings”, find the “Options” tab and click “Configuration Parameters”
• Set the “ctkEnabled” value to false
• Set the “scsi0:x.ctkEnabled” value to false for each disk of the VM in question
• Open the source folder and remove any -CTK.VMDK files.
• Power on the VM
• Power off the VM again. This step is needed to update the CTK table.
• Power on the VM
• Re-run Backup job.