Try to install an image (OpenATV) from the menu option "Network Multiboot Image Upgrade".
You will need to use a cable to connect your box to the router via LAN, otherwise it won’t work.
If you still don’t succeed, then you’ll need to install a Recovery Image (in Slot1 by default), but you will lose the other slots as well.
Afterwards, you can restore the backup images.
It’s always some kind of solution, but I’m a supporter of the idea that if something is supposed to work – it should work. Well, maybe a solution will come up eventually.
