I've finished all the main companion quests (including Glory of the Dead). I want to cure my lycanthopy, but when I try and activate the Flame of the Harbinger, it doesn't work. I have 4 (of 5 total) witches head. Is this a bug or is there some missing prerequisite?

Thanks!

I tried the same thing countless times, it wouldn't work on me either. Then I asked Farkas to give me a random quest, and while on that quest (before going to the bandit site) I went to the Flame of the Harbinger and it activated, so I killed my wolf spirit and cured myself. Try it and see if it works

Minor Spoiler
I had the same problem too, what you have to do is do those random quests for Farkas and Vilkas and eventually they will want to cure themselves and want you to come with them. After you cure them you can cure yourself. Worked for me. Try this if the above post doesn't work.

This also happens sometimes if you haven't cured both the brothers. That quest, however, is also bugged and sometimes one of them won't give you the quest. There's a workaround to force him talk about jobs that involve taking Aela as companion and teleporting you and her to his location... how people discovered these workarounds is beyond me but it worked for me and, afterwards, I was able to cure myself of lycantropy.

Note that, even if you're cured, some people report that the "well rested" bonus doesn't work as it should and that the "Days as werewolf" counter still keeps on counting. On PC, this can be resolved by typing in the console "set PlayerIsWerewolf to 0". Even with this, guards will still joke about your foul smelling breath, wolfish grin or fur coming out of the ears.

The amount of bugs in this quest is unbelievable.