So the basic idea is:

1) Went to Saint Coinach's Find - opened up the trial levequest process.
2) Somewhere, somehow you 'abandoned' the actual levequest that you needed to do. (Clearly, from the "Levequests 0/16" on your screen)
3) Now you can't abandon the original quest as shown above nor can you accept the levequest again to complete it.

Does that about sum it up?

Sounds like a bug or incomplete work to me. I'd file this over in the bug report forum, it may be the only way to bring some attention to this.

I like puzzles; this is has me stumped.