Arrrgh. I definately know the problem now. I had a clear out on my pc and thought I had duplicate rom folders so deleted one. I was left with my amiga forever kickstart roms. These are encrypted and will not work on whdload on a real amiga. They're meant for an emulated environment. 
Game over...
If you ever run into this problem, all you need to do is start up an emulated environment using the encrypted ROM and then use a Kickstart grabber from within the emulation. As long as the drawer where you save the grabbed ROM file is accessible by the host system, you'll have yourself an unencrypted ROM.
