Can anyone help with a midi problem?

I have a m-audio Keystation Pro 88 that I use on a MacBook Pro with Logic Pro 7. I have an SP-2 sustain pedal, and it stopped working correctly some time ago. I tried replacing the pedal, but the new pedal has the same problem, so the issue must be elsewhere.

The pedal won't function in continuous mode (like a normal piano sustain), only in on/off (one press to turn on sustain, another to turn off)

I've tried both sustain inputs, assigning each to controller 64, but no change. I've flipped the switch on the bottom of the pedal, no change.

Help please!