that is because you have an older card revision any card bought now will work on your 3DS the new cards don't need the pcb line cut just the first 2 revision's of the R4i 3DS RTS flash cart need that done any card after that works without a problem, I have the third revision card I just ordered 2 more for my step-brothers for their 6.1 3DS' and it works without a problem.
Heres a little tip though If you want to go online on your 3DS with DS games yes it does work start up wood press start, select 3DS setup, press "x" then go to your 3DS system menu, go to settings, other settings, DS Profile, it will kick you out of it saying an error has occured don't worry about it go back to wood launch a DS game that has NWC like metroid prime hunters go to Nintendo WFC settings set up a network just remember the wifi access point has to have wep encryption after you set it up you'll be able to go online on NDS games using your 3DS you'll get a DS friend code and everything aswell