To sum up: the server declares a misspelled file type. A quick remedy in case of the most popular server system might be found at http://bignosebird.com/apache/a1.shtml (- no blue clicky on purpose).

(Leeneia's method always works, on almost all systems and browsers. Also, every browser can be configured to react to any MIME type declaration as the user pleases.)

I second Jack Campin's plea for ABC versions if available, not instead of MIDI, but additionally.

Important for both formats: precisely matched lyrics, at least of the first verses, would be great!