Whether you have MP3 or WMA files shouldn't matter. I have all MP3s on my Keg, and no issues whatsoever.
If you have a habit of taking the DMS in and out of the Keg (as you may want to in case of very cold temperatures), it can be that you have to disconnect/reconnect to get it going again. But if you're leaving the DMS in and it's still happening, there's probably a loose connection somewhere.
Be sure to screw the cable all the way down when connecting to the Keg, as asdf wrote. Assuming you are doing that, then there could a loose connection on the inside of the Keg. If you can get it out of the car, you can easily open it up and check for yourself.
Also, make sure you have the latest Audi firmware installed.