After much forum trawling I worked it out
the DS Fire card will not work with a Mac. If you upload to your card from a Mac, it causes this problem.
I ended up putting my files on a usb drive, then to a pc, then onto the firecard - it worked.
I had this problem "Problem: When I try to load the menu, it has an xmenu.dat error."
So I followed your instructions. I uploaded all the files from the .rar
But when I go into my F card > MENU I just get white screens and nothing. There is no way to load the update file Fire_eng_1_45.nds...