B-50

Question

I have a Keurog B50 coffee maker and when I put a k-cup in place it just dribbles out coffee for a couple of seconds and then quits. I pulled out the k-cup holder and cleaned it and it works fine if I don't put a k-cup in the holder. When I place the k-cup in the holder it just dribbles again. At one point the holder started to open so I thought it was finished with it's cycle but it spurt hot water and coffee grounds at me because of the pressure that had built up. Any suggestions?