just checked and i'm running the same version of mame as bazza.
i'm unzipping both contents of the 2 files into 1 file then zipping that up and putting it into the rom folder on my memory card.
still getting that error. i'm using win7 on my pc though i don't think that will make a difference.
don't know where i'm going wrong tbh

edit: I'm taking all the contents of one file and mixing them with the contents of the other, do they need to be in seperate folders but zipped together in a single folder?

EDIT : got it working now reread thread and pointed me the right way