Just a quick note: I upgraded my ePO server to Server 2008 R2 SP1 today with IE9, and I should have known better. Once the updates were installed, I ran ePO and got this: “The browser you are using is not currently supported.” Great.
After an appropriate period of freaking out and googling, I noticed the last post on this page: ePO 4.6 with Firefox 4.0. “While IE9.0 is not officially supported it can be run in compatibility mode.” Doh! Why didn’t I try that! Clicking the little “Compatibility Mode” button did the trick! Sweet deal.