So, the Greybeards sent me off after a word I already have. Now I can't complete the quest and move on to the next word. svcks the Game somehow didn't recognize which words I did abd didn't have.

Which word?

Drain Vitality from the wall at Arcwind Point. One of the new shouts that came with Dawnguard. I tried shouting the word to see if it finished the quest, even returned to the Greybeards and, nothing. I found the word on my own through exploring. So I'm not sure why the Greybeards sent me after it again.

Very odd usually this bug occurs when you say unlock the word of fire you learn from paarthurnax before he gives you the knowledge. This causes a second word of power to be unlocked. Which can be a problem as it makes it possible to have the shout fully unlocked without visting Sunderstone Gorge.
A similar thing can happen with other free words but Drain Vitality isn't one them. Now your sure you've gotten the word already from arcwind point and not one of the two other locations? Assuming yes my only advice is reload a save from before you accepted the quest or you'll have to look up shout locations manually.

I am absolutely sure it's Arcwind point. That's where the quest is sending me. I even looked up the location and the word in my strategy guide, yup. I have it, it's Drain Vitality. Walking up to the wall does nothing. Guess I'm going to have to do it manually with the guide then. Stupid bug. Hope Beth can fix it.

Sounds like a crack in the radiant quest system as this particular wordwall did not exist before Dawinguard.odd though, such do not usually send one to a wall one has been to.

If it means anything I had a courier appear and send me back into a dungeion I had just cleaned out.
You were heard shouting in , go find the source of .

I think these quests may be borked in general considering this note referenced to and pointed me to the place I had just cleaned out.

This just now happened to me to actually! Well not the whole being sent to a dungeon I cleared part, but as soon as I left Arcwind point and went back to Riverwood, a courier, who for some reason was completely naked, gave me a note saying I had been heard shouting in Arcwind and the note wants me to check out a source somewhere.