Q: I got the rom image has crashed, what did I do wrong?
A: Nothing is wrong with you. No$GBA works only with encrypted roms, because the nds roms has already been decrypted. There are two tools to your chosen. One is called eNDryptS Advanced which can be found at: http://www.gbadat.altervista.org/tools.htm
or another one is called NDSTOOL and you can use dslazy gui with NDSTOOL for windows user and can be found at: http://wiki.pocketheaven.com/Ndstool
. The either way will changed your nds roms to encrypted without a problem.