Looks like you have to put file "113-AD38900-101.rom" in the same directory as your "FlashBIOS.exe". The .exe is the tool to flash and the .rom contains the new BIOS. Download the .rom from Asus.
I just updated my HD7950 Vapor X to the newest BIOS. I just followed the ppt that was included and it went flawlessly. Just read the instruction carefully for your make of board.
Looks like you have to put file "113-AD38900-101.rom" in the same directory as your "FlashBIOS.exe". The .exe is the tool to flash and the .rom contains the new BIOS. Download the .rom from Asus.
This is the file i download from asus, which is not a .rom file, but an application and I can't see the rom anywhere on the web.
Sorry for the late answer. In this case contact Asus tech support. Open a ticket with them and they will help you.
From what I could see from the link you provided this is a .zip file containing a .exe file. You probably need to extract the .exe from the .zip before executing it. Once extracted and saved somewhere else, the .exe probably contains more than one file and is probably self-extracting so I don't know why a file is missing. As I said if you keep having problems it will be better and faster for you to get help from Asus.