The AC is the most sensitive HuCARD. Back in the day I knew people that used diving board converters and such with zero issue until they got an AC and then had problems. It even seems to effect certain games more than others, although I'm not sure if that's actually true.
Clean the shit out of the thing, and your system. Use "contact cleaner" made for electronics, not Brasso or anything designed to put a cosmetic polish on things because that's just going to turn into more oxidation at some point. The pencil erasure thing works pretty well too, but be careful to not scrub too hard and rip up the contacts on the AC.
Then of course there is the other side of the equation, the system itself. For that I take a HuCARD sized piece of plastic (I use Evergreen since I build models and lots of the stuff) that is slightly thinner than the real thing. I wrap apiece of 800 or more sanding film around it, soak it in contact cleaner, and slide it in and out a bunch of times. Do not use sand paper made from actual paper since the shit will fall apart and leave paper/grit in the system. Sanding film is made of plastic and washable.