Check the details of your cart again.
I remember that when I was surfing, looking for my AR+ , which hasn't arrived yet, and I ordered it at august 17th 🙁 , there were some carts announced as 4mb ones (in the big letters). The problem with them was that in the "details" or in the manufacturers home page they said "for save your games" and stuff like that.
Another thing is that you aren't plugging your cart correctly. Sometimes I get errors and malfunctions because of this with one "4th" party cart (just has the word "goldenfinger" written on it), which allows gameshark codes, have backup memory and is country converter.
By the way, I have 2 AR+ which doesn't boot, no matter what I do with them (I don't have a PC comm card to flash the bios, assuming that it is the problem). If you find out how to repair your cart, please let me know.