Backup agent may crash during backup operation which will cause the backup to fail. The below event may occur in the application event log on the DC:
"An unhandled exception occurred in the function: CRequestProcessorImpl. A crash dump file will be generated"
The error shown in the RMAD console may be:
"Unable to execute request (133). A communication error has occurred. The handle is invalid"
This can occur when files in SYSVOL have files with ADS (alternate data stream) with names longer than 54 characters.
Download the below hotfix for the installed version and install it using the instructions outlined in the included ReadMe file:
Recovery Manager for Active Directory RMAD 8.6.3
Recovery Manager for Active Directory RMAD 8.6.1
If you have already applied the hotfix, or are using a version later than 8.6.3, try uninstalling and reinstalling the backup agent if you are using preinstalled backup agents.
If manually running the backup is successful, try changing the backup schedule to run at a different time.