I had this same issue.  I parsed the registry on the affected machines and found a stale service called Smcinst (Symantec Auto-upgrad Agent).  It pointed at the file referenced in the backup log.  The file does not exist.  It must be something Symantec removed from SEP as it was updated.  My affected machines are still running SEP.

Purge the following registry key, reboot, and you should be good

HKLM\SYSTEM\CurrentControlSet\Services\Smcinst

Don't do that. It's likely the EXE only exists when there is an actual upgrade to perform to Endpoint uses auto update (for example the recent MR). Just add it as an exclusion.

Unfortunately you still get the error message if you exclude the files. I even removed the c:\program files (x86)\symantec\symantec endpoint protection\smclu\ directory and still got the same message. The stupid thing is in my case the file does not even exist

the EXE has just moved from

C:\program files (x86)\symantec\symantec endpoint protection\smclu\setup\smcinst.exe
to
C:\program files (x86)\symantec\symantec endpoint protection\smcinst.exe

I've re-pointed it to the actual file location.

Backup Exec can sometimes see similar errors for files from all sorts of applications - it is caused by another appplcation/program registering a component with the system state and then not unregistering the component when it is removed - in this case it happened to be another Symantec product so posting in the forum (or logging a support case) against that product might have helped. With the case of 3rd party software we would recommend you contact the vendor to sort out the problem.

There is a quick an dirty fix of create a small text file in the folder with the same name - but this is a workaround and not really a recommended solution.

Of and BTW the file exlusions option in the backup selection list only applies to backups of the file system itself (C: D: etc) the System State does not use the exclusion list which is why adding to the exclusion list did not get rid of the problem.

Colin, so you and I both know this is caused by LiveUpdate not working correctly and leaving traces behind when it runs. Your posting implies that there is a *real* solution to this  - what is the fix?