"Purity" quest problem

[human resource]

When I talk to Vilkas and go through the dialogue that starts the Purity quest, the game does all the usual stuff related to starting a mission, but then he won't follow me outside Jorrvaskr and as soon as I travel twice (e.g. Jorrvaskr to Whiterun to Ysgramor's Tomb) the quest becomes greyed out and inactive. This has happened three times already and I don't quite know what to do.
To elaborate: When I start the quest in Jorrvaskr he does follow me around and the map marker is in place, but when I go outside the marker is gone and Vilkas stops following me. When I tell him to follow me (the usual follower line) he says I've already got someone when that is not the case.
I tried a workaround by luring him all the way to Ysgramor's tomb by clearing the follower count and recruiting him through the console but still no luck getting the mission to actually work.

Any ideas?

[Eternie]

With the companions quests you can have a couple of quests if the other quest ... possibly from Aela or Farkus hasn't been done that may happen. In which case complete all quests from any of them .. search through your miscellaneous quests ...and complete them first.

The other thing obviously with vilkas is reload a save before you talked to him ... then wait till his morning workout say 10 am in the courtyard so he is outside when you talk to him. If the marker works .... then don't fast travel but keep him with you all the way! Should work!

[rallicknom]

The same thing happened to me. I finally solved the problem by doing the Purity quest with Farkas first and after I had completed that Vilkas would follow me to Ysgramor's Tomb.

[human resource]

I finally got Farkas to offer his instance of the quest (took quite a few Family Heirlooms and other pointless radiant quests before it finally popped up) and that worked just fine, so hopefully Vilkas' version won't cause any more trouble once I get around to doing that. And if it does it's not a huge thing, my primary goal was to get rid of lycanthropy myself, which I now have.

It's a little silly that apparently this exact thing has been a problem for many people yet it never got patched.

[Eternie]

The process is described in The UESP which usually has the answers your looking for with any quest or glitch, they do a brilliant job in helping people with many games They also suggest if your javing Vilkas troubles to just ask him to follow you then take him into the tomb, once there dismiss him Save and ask to get the purity request .... reload if a radient quest comes up.
http://www.uesp.net/wiki/Skyrim:Purity