Have the same problem with some of my clients' that have the T2i. We have been slowly replacing them with the, more stable I think, T2x. Called tech support on this issue and to unfreeze them you have to reset the remote.

I believe you have to hit the 'OK' and the backlight button on the bottom at the same time. Keep them down for about 20sec and then the remote will turn off. Hold down the same two buttons to turn the remote back on.

There is also a limit to the number of characters/letters you can place on a button that is active or inactive. I believe the number of characters that you can place on a button is 15 or less. This information was given to me by RTI tech support.

Hope this helps