Can't change film speed on Metz 54 Mz-3 with M6 TTL

<p>I'm experiencing a strange problem I've never had with my 54 MZ-3. I loaded a roll of 200-speed color print film in my M6 TTL, changed the speed dial on the back of the camera to ISO 200, loaded newly charged batteries in the MZ-3, turned on the M6 TTL and then turned on the flash. The ISO on the flash read 50, so I attempted to change it to 200 but the wheel would not change the reading. I then turned the camera and flash off, turned the flash back on, successfully changed the ISO on the flash to 200 with the wheel, turned the camera back on, and the flash ISO immediately switched back to 50. I then cleaned the contacts on the 3502 adapter and the hot shoe of the M6 TTL with isopropyl alchohol and a q-tip, but the same damn problem of the flash reverting back to ISO 50 recurred. Any suggestions about how to fix this nightmare?</p>

<p>Addendum to above: I just noticed that when I take my 1993 50mm Summilux off my M6 TTL(which was on my M6 TTL when the above problems occurred) and replace it with my 1999 90mm APO/ASPH Summicron, then I can change the ISO setting on the Metz flash to 200, but if I remove the latter and again put the Summilux on, the ISO setting on the Metz changes back to 50 immediately. Gads, what is going on here???</p>

<p>Solved! I suddenly noticed that the metal contacts on the hot shoe of my M6 TTL were discolored and also then suddenly remembered that I had gotten rid of that discoloration in the past by rubbing a pencil eraser back and forth on all three contacts. I then did that, and now everything is fine! Yay!</p>