I've had problems in the past with word processers which automatically double space lines (Even if you are copy/pasting an earlier text).
This can prevent ABC from working, whether in the various headers, or in the tune itself. If this is the problem you need to go to the beginning of each new line, backspace, so that it shows as a continuation of the previous line and Shift+Return to make it a single carriage return rather than a double.

Alternately copy/paste it into an online ABC converter such as Mandolin tab and see whether it performs correctly there.