I had the same problem, which is funny enough as I use the same NTFS USB 3.0 drive for my Bios updates for the exact same mobo since I bought it (8 months now)
Anyway, although I did the 2501 bios update without problems, I wanted to go back to my most stable build I had with 2203 version cause of some unstable problems I encountered with that version of bios. When I tried with the same method, I received the same error message as you did.
What it did the trick for me:
1. I formatted the USB flash to Fat 32 from windows option and I make sure NOT to be a quick format
2. I copied the Bios in the flash and rename the file into C7HWIFI.CAP
3. Make sure you insert the flash drive into the USB Bios Flashback Port (you can check which port it is from the manual - the first left USB port as you watch the back of the mobo in case it is vertically installed)
4. You can either do it by pressing the Bios Update button for like 3 secs OR entering into the Bios as you normally do and set it from there (I did the second option)
In any case I hope this short guide to help you with your need.
Friendly
Oldar