Andy, we have a k50 model for home use and it will do this from time to time (we've had ours for about 4-5 yrs now)
What I have found useful is to unfurl a paperclip ...
that 'pin' that pierces each K-cup- there's a very small hole in it (that's where the water comes out), poke that paperclip up in there a few times and then run a cup of just water through, no k-cup pod, that should do it...
If not, unplug the unit, take off the water reservoir and the cup platform, open the handle as if you are going to place a pod, hold the entire machine upside down over the sink and give it a few good shakes... water should come out. Ensure that the filter-thingy where the water reservoir sits is clear (you can just run your finger around it or a lint-free cloth to ensure there's no calcium) , also the filter in the reservoir itself. With all that said, you should be good.