I'm not sure when this started but I noticed that my Exchange Server's POP3 and IMAP4 services were no longer being started. When I would manually start them I would get 'Error 1083: The executable program that this service is configured to run in does not implement the service.'

I found the Q277770 Microsoft Knowledge base article which addresses this and fixed the problem. However I still do not know what caused this as it was working at some point in the past.