are you following this guide? https://github.com/RetroPie/RetroPie-Setup/wiki/Managing-ROMs follow the accompanying video and use the .dat files provided on the wiki page rather than the ones in the video. Are you trying to create roms for mame, advmame, pifba, libretro-fba, or gneogeopi?
Reply To: New user – Converting – What am I doing wrong?