SMB4MD (Super Mario Bros for Mega Drive)

[Strider_Hiryu]

It may just not be compatible with your flashcart.  I've seen quite a few homebrew games that have that problem.

Looks like the ROM have a problem, because some guys were trying to make a repro cart, but they failed too 

[Tailsko]

This is a win. I like this ^^

[MarioMania]

The ROM needs work to get on a Cart

[nintendodork]

Well, take for example the Super Mario World Famicom pirate.  It's exactly like this game in the sense that it can't be reproduced on a cart or played on a flashcart because it may just have an odd mapper that so far, no one has seen any donor boards with the correct one that they could use for it.