Ah, the old milkytracker save bug. Go back a version x.x.85 or something.

MilkyTracker version 0.85 is what I used to make this song. when I said MilkyTracker was being a big baby on saving MOD files, it always complains about some invalid pattern data every time i click the save button.

I was attempting to edit my previous comment but it didn't go through. Anyways, this is what I was going to edit in. From what I've seen, some of your notes are above/below the C-3 and B-5 restriction. You'll have to sift through the drum section as I've seen quite a lot of C-6 notes in there. Once Milkytracker doesn't give you a prompt, then your .mod file will officially be a .mod file.

there are versions of the development build which fixes this problem linked in the main thread.