This is my first post!
I think the problem is that some people don't know you need to hold down the mode button while you are turning on the system. People have said hold it at start up but I think some are confused.
Also, Ms. Pac ABSOLUTELY has to have the mode button held down to play it with the 6 button. I reviewed this at Sega-16 years ago and I had to do this. Once it boots up with the controller in 3 button mode it works just fine.
Oh yeah, one more thing. I am aware of at least 2 different versions of Ms. Pac on Genesis. One of them has yellow letters on top of the cart, the other has pink letters. Don't know if this makes a difference, also don't know if this applies to other regions.