Try cleaning the contacts on the cart.

 

Just a damp towel, cloth or paper. Not wet enough to drip if you squeeze it. I've also seen pencil erasers recommended for cleaning contacts, but you'd probably have to cut one up to get it in the cart.

Whatever you use, make sure it doesn't leave little bits of itself in the cart.

Just to be clear, I'm talking about the G6, not the DS. I don't recommend sticking any of those things in the DS cartridge slots.

 

I'm using 4.6c without any such problems. I've heard of some other problems with 4.6b & 4.6c, but nothing like that. It sounds like the cart is barely making good enough contact most of the time, and every once in a while the contact fails just long enough to crash the game.

As far as the odds of getting a bad cart, I'd say fairly low, but it does happen. The problems tend to be more obvious like half the flash memory fails so the cart is only 256 MB, or the battery fails so you can't save, or it just dies altogether.