WSUS unable to delete log file.

One of my WSUS boxes had a log file in the C:\Program Files\Update Services\LogFiles directory that was 60MB big – normally these are deleted by WSUS itself, with a backup copy of the previous log kept as SoftwareDistribution.log.old. However the permissions on the folder were set such that Network Service (which WSUS runs under) did not have permissions to create new files in the directory. As it could not create files, it was unable to move the existing file to .old and create a new logfile to start writing entries in. By granting Network Service change permissions to the C:\Program Files\Update Services\LogFiles directory and then restarting the Update Services directory, the SoftwareDistribution.log file was renamed to .old and a new file created. Inspiration for this was found at EventID