These are from some old posts. See if one or two will work for you.
Be sure that you have:
- talk to Bryda to know about the messenger's function and about the magic scroll.
- talk to Sir Wrathling, Nuri and group leader.
- look at or jump to all the spots on that overhead map first and look around (to know all the places).
- then follow the messenger by looking (overhead map) where the moving light is located.
- once you located him - then use the spell.
- try different ways or position to talk to the messenger. It might be that your cursor is not active at the right spot.
Also if that doesn't work - try going back to a saved game and follow that messenger.