Okay, so I have recently got back to using my 3DS and I wanted to use my DSTWO. After a friend of mine I lent it to updated it meant I had to source a DSLite which was reasonably easy. So after updating it with the newest firmware v1.25 if I recall correctly I then put it into my 3DS. It was not recognized so I do the usual. I clean the contacts, blow into the 3DS slot. Try out another game to eliminate the 3DS as the problem. I then reinstall the EOS, again no luck. However it works on the DSLite perfectly so I do not know what is wrong. My 3DS version is 7.0.0.