Some new information in on client troubleshooting - A Customer has  reported one or more clients failing to install updates with an error 0x80070005.  Investigation shows this issue to be related to a DCOM access problem.   The root cause is is related to either  an incompatible default DCOM impersonation level, or corrupt default access permissions on the client.  A KB is in the works; draft information about the issue can be found on the WSUS wiki at: http://www.wsuswiki.com/80070005.