If you've been having problems locating the root cause of problems with your WSUS infrastructure, be aware that a number of log files are available at both the client and server:

The Windows Update Agent has a log file “%windir%\WindowsUpdate.log” with verbose logging on updates that have been installed.

WSUS 3.0 has a log file “%Program Files%\Update Services\LogFiles\changes.log” that contains a record of all recent approvals and who made them. If the approval was created automatically (e.g., auto-reapprove revision, auto-approval rule, or auto-approve WSUS updates), the user in the log will be “WSUS Service”.

A third log file on the WSUS server itself is “%Program Files%\Update Services\LogFiles\SoftwareDistribution.log”. This log provides information about the software updates that are synchronized from the configured update source to the WSUS server database.