I've been messing with this for two days now - I've run though all the articles and all the EE posts which pertain to this issue with no luck. I did however just get this message while looking into settings under Session State and I'm not sure if this is related or not.
"There was an error while performing this operation.
Filename: \\?\D:\Program Files\Microsoft\Exchange Server\V14\ClientAccess\owa\web.config
Line number: 38
Error: Configuration section not allowed to be set below application