I've had the same problem and found no documented solution or cause. Calling Tassimo was no help. However I've noticed that it usually happens after trying to close the unit when the T disc was not lined up correctly. This pierces the foil in the wrong place. If you run it like that, OR if you open it back up, line the T disc up and reclose; it will spray water and coffee grounds all over. It seems some of the coffee grounds or a piece of foil from the T disc can get stuck in the little switch on the left side bottom of the closing mechanism. This switch indicates to the machine that it is closed. So if the switch gets stuck closed, the machine can think it is closed when it is really open. This prevents a failsafe interrupt from operating which would normally stop the pump and reset the stuck faulty logic in the machine. So the solution is to clean the machine very well in the area around the T discs. This includes removing, cleaning(inside and under), and replacing the part that pierces the T discs. It may look like it is all one piece, but you can pry it up with a butter knife.