Hi.
The instructions are fine, and this should work okay. There are likely other issues.
Giving it one more go, if you haven't, may work ... you could've made an inadvertent mistake that caused this.
brokenfile.php occurs when you attempt to link to a non-existent URL.
- I was able to reproduce it by manually screwing up the URL when editing.
- It is unclear, aside from inadvertently and manually messing up the URL, what normal process would cause this. I haven't looked at the code, but have looked a fair bit at moodle.org, to no avail.
- In my experience, one cause may be session/timeout issues which prevent proper saving.
There'd be other symptoms, like the improper saving itself, or being logged out "by Moodle." It likely screws up the saving process, and the target URL is never created. - Copying and pasting a URL to a file from within another resource/activity/block.
This likely applies to the editor URLs, with draft in them, as opposed to the post-saved URLs. Editor-based URLs are local to whatever module you're editing.
My guess is the URL isn't much help, at least not w/o really understanding the code, and even then, it may just seem random to a user.
Cheers