I was accessing an Outlook account when suddenly I got this error on the Win 8.1 machine.
Outlook Web App doesn't support this type of client computer.
I am able to access the same account from WIN-Xp or Android so I have the id and password, and url.
One odd thing I noted is that the option to select the Light version is grayed out. I have tried to clear the cache to reset things. Is there possibly an outside cache in addition to the IE browser?