That is truly strange. If you typed it right and it's in the root directory like I described, it should just WORK. I'm totally stumped by this one.
It sounds like it can't find the file, but if you did everything I said, there's no way it couldn't find it.
I'm about ready to just say throw in the towel on this one, and get a new mobo if you want to use the new CPU. That comes with a MAJOR caveat though. You'll HAVE to reinstall Windows. If you don't have another copy, that's a problem because the OEM install is tied to the original mobo and even if you could reinstall it, it would fail validation, so you'll have to decide what to do from here, I guess.
None of that should be necessary, but it seems that updating the BIOS on that motherboard isn't going to be possible.