This is a known problem with the micro switch buttons that are soldered to the internal circuit board. The buttons wear out and need to be replaced on a fairly regular basis.
I submitted a fairly lengthy post with all details of how to do this but the post has expired. In summary, you need to open up the Short Board and de-solder the failed switch from the circuit board, then solder in a new one. The switches are very cheap and can be sourced online or from any electronics supplier.
Next time I open mine up I will take pictures and re-post the instructions since this seems to be a fairly common problem.
This was the post in case anyone from Line 6 is paying attention http://line6.com/sup...e/366052#366052 but as I said, it is no longer there.