Error when running backup: "cannot establish the connection to the backup agent" (4296804)

Error when backing up: "Failed to connect to backup agent: cannot establish the connection to the backup agent"

Try the following possible solutions:

1. Check the scheduled Windows scheduled task passwords. Rright click each task and select Properties.  Select the "Change User or Group" button.  Verify you have the right login here
2. Change the password on the Agent Settings tab in the properties of the computer collection (verify password is correct)
3. Ensure the account being used has the correct permissions to back up the domain controller
4. If a preinstalled backup agent is being used, verify that port 3843 (default port, it's possible another port is being used on the agent) is open from the RMAD server to the DC. A firewall blocking the port could cause this error
5. If there is a firewall enabled on the DC, ensure it is allowing the Backup Agent exe found under c:\windows\RecoveryManagerAD
6. Check to see if a new group policy was implemented that is preventing task scheduler from running - Run as a batch job.  Update the GPO and add the service account to run the scheduled jobs
7. Try changing the backup schedule start time to start a few hours before or later than the current time
8. If the permissions are fine and the port is open, verify that NTLM is not blocked in the environment. Refer to https://support.quest.com/kb/38136
9. If the target server being backed up is an AD LDS (ADAM) server then the service account running the backup should be a local administrator of the AD LDS server
10. If there is a Trust between the RMAD server and DCs, ensure there are no issues with the Trust communication between those servers

Enable the setting "Connect to the backup agent using specific TCP port" in the settings menu.