OK, have hit a problem.

I created a simple custom convert file using Notepad just to test that it works, but got this error message when attempting to upload it:
[ERROR] Invalid file format, must be a text file"
Thinking perhaps it might be due to Windows using CR/LF for newline, I removed the CR characters using a hex editor and tried again, but with the same result.

Any ideas?

Here is the full content of the file I was trying to upload:
flc flc * *
	[sox] -q --multi-threaded --no-clobber -t flac $FILE$ -t flac - remix 1 0
Are there any header lines I need to include? (The "invalid file format" messsage would seem to suggest it's nothing to do with the content, but a more fundamental issue).

I'm using an old pCP (v4.1.0), if that's relevant. Was hoping not to have to upgrade, but will if it's required.