If you had another switch and it worked, it would prove that your switch was the problem. If it still didn't work, the problem could still be in the amp or in the cable.
If you'd like to check the cable... if your multimeter has a continuity check, use that setting. If not, just set it to measure resistance. With the cable detached from both the amp and the switch, touch one of the pins with one of the probes and touch the same pin on the other end of the cable with the other probe. It should have connectivity or shouldn't measure more than a few ohms of resistance. If there's no connectivity or the resistance is high or infinite between the same pins, then I'd suspect the cable.
This is assuming that the cable is a straight connection (e.g. pin 1 = pin 1, pin 2 = pin 2, etc). I'm not sure that this is the case, but it most likely is the way the cable's wired. Bogner could confirm this...
But, if you do find a problem with your cable, let me know and I'll verify your findings against my cable. If you don't find a problem with your cable, I'll see if there are some measurements you could take on the amp's footswitch jack. In any case, you should be able to determine if the problem is definitely the switch, the cable, or the amp with just your multimeter.
I know that it seems unlikely that either could just go bad without being moved. I've seen it happen, though. Sometimes, if a solder connection isn't good, or if there's a weak spot in the middle of the cable, just the stress of gravity can eventually be enough to cause a short. Differences in tempurature and humidity can cause the insulation to dry and warp. And just using the switches can send small mechanical shockwaves through the jacks and cable. Regardless, this doesn't happen very often, but it does happen.
A couple of other things you can try...
If you have some Deoxit, you can try cleaning the jacks on both the amp and the switch. You could also try cleaning the switches by removing the back cover of the footswitch and spraying some Deoxit in each switch.
Also, with everything connected, wiggle the cable and see if the lights on the switch flicker. If so, the problem is probably in either the jacks or the cable.
Anyway, good luck with this! I'm sure that you'll figure it out!!