I don`t know if I much of a help, but I read, that SNES roms can`t be larger than 4 mb. I think this is because of the 8 mb ram of the gp32. So perhaps thats the error you get.
Oh and, yeah, it would help if you post which rom for which emulator you use...
Please correct me, if I`m wrong. PLEASE!!! I`m a liitle bit angry because my GP32 should arrive this morning but it didn`t so I have to wait another day
EDIT: Oh sorry, I got to this thread via the news on gp32xtreme and didn`t notice its the support for GP Advance. So, if any mod wants to, delete this post.