QUOTE(AddisonStSox @ Jun 12, 2005 -> 12:28 PM)
Is there a way to set that as the default media player?
Sure. Just open up RealPlayer, then tools > preferences > content > media types.
You can select it to play everything if you wish.
If you would just like to use RealPlayer to watch MLB.tv, just hit preferences in the MLB.tv window (if you can get this far with your current error), and then select RealPlayer as the default viewer.