Thanks for chiming in, Jorpho and Bonesy.
So that was the reason, it was an nkit file. No wonder it gave you errors.
You see, tools like Delta patchers or Beat take notice of the original file when you create the patch, so when someone tries to use that patch it checks your game file to see if it's the same that was originally used. It is a safety feature so we can be sure that the patching went well and the result is a full working rom or iso.
Nkit files are GC (or Wii) games compressed with a new algorithm made by Nanook, and while you might use it as a nkit file on some places, the data inside the file is different from a normal iso, so when the Delta Patcher checked your nkit file, it just did not match. That's why rom hacks are shared and uploaded with information about the original game image used called checksums, and you can check if they're the same with Hex Editors or tools like 7zip for example.
In fact I think nkit format didn't even exist back when I did my hack!
In any case, it's good you got it working. I hope you have fun, and now I'll go hide back under my rock again, lol.
To all of you, have a nice day.