That's a new one on me. Just a guess, but it can probably be recovered by installing the bootrom again and/or by loading EXOS again from the bootrom prompt.
If you want to try to recover it, GTAC can get the bootrom file to you and should be able to provide a set of instructions on how to load it when EXOS won't boot. I'm not in the office today so I can't just send it to you 🙂
