It is a deep area where your IT staff gets to work. I have yet to see a single cause or cure but most often it's some permission issue or the "server" has run out of handles. There are also patches and hotfixes that MSFT only shares with you if you call in.

As you have done the usual it's time for the IT staff to call it in and gain access to the stuff MSFT doesn't put on the web.
Bob