SharePoint 2007 Web App backup fails with error "Directory <Unknown> was not found"

I'm backing up SharePoint 2007 with BE12.5 sp2. 

I'm receiving one error during the SharePoint backup:

Final error: 0xe00084af - The directory or file was not found, or could not be accessed.
Final error category: Job Errors

For additional information regarding this error refer to link V-79-57344-33967

Directory <Unknown> was not found, or could not be accessed.
None of the files or subdirectories contained within will be backed up.
Directory  was not found, or could not be accessed.
None of the files or subdirectories contained within will be backed up 

If I modify the backup job, unselect the SharePoint Web App where the error occurred, save the job and then reselect the web app/save job, the error disappears.  Only to find the exact same error moves to a different web app on next backup.

Occasionally I can get the error to disappear, then days, weeks, sometimes months go by without error and suddenly without any change the error appears again on a random web app.  

It appears the backup job is still successful but I don't feel comfortable with any sort of error duing backup.

Anyone have any ideas?