iTunes: MIDI files cannot be converted in iTunes 6.0.3 - 6.0.5

Attempting to convert a MIDI file to another format in iTunes results in an alert message:

Error occurred while converting the file "filename". An unknown error occurred. (-50).

Solution

If you have QuickTime Pro, you can export the MIDI files in QuickTime Pro to another audio format (such as WAV or AIFF) using QuickTime Player, and then convert those files in iTunes.

This document will be updated as more information becomes available.