My M card is not connected?

[INTERPOL]

I turned on my DS last night and started my Leaf Green Version. I pressed A at the start screen. Instead of finding the continue, new game and mystery gift options it said "Your(or The. I can't remember) M card is not connected." and automatically started a new game when I pressed A. I freaked(or is it froke?) out and turned off my DS and pulled the game out. I blew on it and put it into my GBA and it worked fine.

Why did this happen and what is a M card?

[Black Ice]

Only thing I've ever heard of like that is the 1M sub-circuit board. I have no idea what that is, though. It happens on FireRed ROMs all the time, but I'm not sure why your actual cartridge would do that. It's not even FireRed.

[Hamako-chan]

Its nothing to worry about, that always happened to me. I was like you when it first happened to me, but then I soft reset it and it went back to normal.
I don't really know what happened but I just did the same thing everytime it stuffs up again.

[pokefansam]

Nothing happened to it it just was dirty