Yes, the chin release button is a button on the lower side, where you can attach the release cable. The levers connecting it to the whole mechanism are designed not-too-well, so it's possible to bend them (when someone presses hard on the button while it's locked by camera or the shutter was not loaded). That causes the problem, and usually it's easy to find and fix. And the sticky release cable causes the same even on healthy bodies of C330, otherwise perfect machines.

Good luck,
Zhenya

Quote Originally Posted by thebanana
I had exactly the same problem with my C330. It's now in for a CLA. I'll let you know if that made any difference. By the way, what's a chin release button?