That same thing happened to me with the Ms.Splosionman beta. In the main menu it said 'Unlock Full Game' (or something like that*-)) and when i selected that option something like your picture came out. I was like "daaayyyyuuuummmm".....
The Gears of War 3 sale. When trying to download the Golden Lancer, which says it's at 160. When you go to the screen before purchase it says -1MSP and when you click confirm it says you need 4 billion points. Maybe because the supposed removal of guns from the marketplace?