Thanks for your quick reply. I do have the TRS cable in the pedal jack. I can see why you might think it was in the footswitch because the expressioin pedal was changing programs when depressed. I didn't command the foot pedal input to do anything before it started changing programs. I will try plugging it in without the expressioinator and clear the internal memory. Hopefully this will do the trick.

Since a few people ar having trouble with GTR4000 pedals we looked into it and this is what we found.

The GTR4000 (and DSP4000) are so old that they need a type of pedal which is not common today.

They want a TRS cable, where the ring goes to one end of the track, the tip goes to the slider and the ground to the other end of the track.

They will not work directly with something like the EB VPjr, which has input and output jacks, nor a pure 2-wire expression pedal.

You can use them with the EB if you buy a Y-cable which has stereo (TRS) at one end, and two mono (TS) jacks at the other. Connect the TRS to the GTR, and the tip lead to the OUT jack, the ring lead to the IN jack.

Note that this pedal requirement is different from our stompboxes, which require a 2 wire (TS) expression pedal.

We can't give advice for other pedals – you must talk to their manufacturers and give them this information.