I did check Symantec Backup log, and there were some glitches. I fixed those but still to no avail. It's not on my server, one of my customers. They also have ADNM installed on that same server which happens to be the DC as well, so rebooting often is not an option. Really odd. As soon as Avast Server is uninstalled Symantec BUE runs fine.
Any other ideas? I also excluded BUE directory from the scan list....