Burning arrow fault

i recently unlocked burning arrow with balthazar rep, and then bought an elite ranger tome and learned it... it was working perfectly fine for a few days, but now a mini lock has appeared over it and i cant use the ability... any ideas of what went wrong and how to fix it?

Sounds like you were using a Nightfall trial, and now it ran out?

yup. you need to own nightfall to use nightfall skills

but the trial ran out a while ago, and i was using the ability this morning

Low Level Arena or Trial Ended.

Well it caught up with you