Whenever I put a Gamecube memory card into Slot A on my Wii, it either says that there isn't a memory card inserted, or that something other than a Gamecube memory card is in Slot A, but when I put the memory card in Slot B, it works fine! What could be the problem, and what should I do about it?

It's probably because dust has collected into that slot. Try rubbing the inside with a cotton swab and blowing in it a bit. It'll work. And next time- keep your memory card in there.

Or......probaly he should use a Gamecube with the memory card instead of a Wii o.o

No, the Wii has had this problem of not reading some Gamecube Memory Cards since it first came out. Usually just cleaning out the dust in both the slot and card as well as keeping the lid that covers the slots(and the controller ones too) down will usually fix any problems. That's the problem with alot of slot based things, you gonna keep em covered and clean every once in awhile.

Oh and boo, going back to not being online for another good few months...maybe

GASPIMISSEDCHIBIGOKU!!!! >_<