I have a problem with Digitech rp255 expression pedal.. The V-switch to be exact..
Well, the problem is that it does not work, at all..
I opened pedal and I think its hardware problem, maybe some rubber is missing on pedal itself so it doesn't make contact to a sensor on unit

Its a optic wah/volume/expresion pedal.
You have to calibrate it. Read the manual its got to be in there .
Also i suggest u get that yours rusty silver thing that goes to the optical sensor ass you rock the pedal back and forth a nice shiny silvery toutch (paintjob).
Expression pedal itself works great, you can "express" wah/volue etc completely normal if you set up wah before hand.. ONLY the switch (to activate wah at aytime) does not work ;P