You have to set the correct save type: FLASH 512 KBytes in Options->Emulation Setup.
Then go to File->Reset. If you intend to play this game later, you can save the setup so that you won't have to do this the following time: go to Options->Save Options.
Acutally, if you plan to play other games with No$gba, in its current state, you have to set manually the save type. Here is for example a list of all game's save type:
http://www.dualscene.net/lists/index.php?listname=Supercard
Note that it uses "bits" while in No$gba, "bytes" are used.