AF540 and K20D Issues

I was doing an industry dinner last night and had my K-5 as the Primary Camera, and the K20D as my secondary camera.
Now the K-5 work faultlessly, but the K20D?
Well, initially on the K20D I had the AF540 flash on it, and things were going well, flash was going off, photos were taken. However, after a while the camera and flash would not talk. Switched camera off and on, removed the flash and re-seated it, switched it off and on, lots of combos of switching flash first, camera first etc etc, but nothing, the flash would not trigger! I was in P mode at the time (the best mode for me for corporate events) but nothing.
I put the flash on the K-5, and everything was fine, totally reliable.
This proves there is nothing wrong with the flash, so I am pointing at the K20D.

Has anyone had a problem with flash and the K20D? Should I send it to Pentax for an overhaul? (probably costly and a second K-5 body might be cheaper, but not with a battery grip.......)

Thoughts?