Hi, Matt -
I've noticed a couple things that will make it so the concertina.net converter won't work:

• You MUST have an X:(plus any number) line as the first line in everything you submit. If that's missing, X:1 will work just fine
• Lines can't start with a blank space

You'll find lots of ABC tunes to experiment with at http://abcnotation.com/.

Holler if you still have trouble.

-Joe-