Thanks for finding this.
The problem happens because one of your media events is missing a media type.
I have fixed this for 0810. To fix your problem, you have to modify your media scenario on the My Scenario page in the web. On the left hand side, click on Show Devices tree (at the bottom of the screen), and then on My Scenarios at the bottom of the screen. Browse thru your media scenarios, and fix the missing MediaType entry.