I have had this problem, in that some of the channels would freeze. I was using a Thompson box.
I either turn the box off from the mains and back on again, which would fix the problem, but moved the box so it isn't near other electrical devices, disconnected all the wires, reconnected them and it's OK now.
You could try this and see if it cures it.
Good luck.
Kenno
May 2010