She just stands there at the alchemy table when its time to activate the soul cairn portal.
This also renders me unable to complete the quest.

She stood on top of the portal for me. Kept saying she was busy. I just zoned to the balcony, came back and it worked fine. If that don't work try restarting the game.

Wont work.
Until its fixed, I can't go finish the quest.

Help please?

I'm having this problem too.

Just fixed it by reloading.

Not fixing it for me. I put all the ingredients in the bowl and she ask me if I'm ready, I select that i am and then she just stands there:(

Re-do the mission.
That fixed it for me.

The entire mission? I've redone the part where you first enter the room and serena looks over the circle then tells you to find the journal a dozen times.

If you are on the PC use the console to advance to the next stage by using the command 'setstage DLC1VQ04 90', its what i did to advance as I too was stuck in a similar situation. In future refer to http://www.uesp.net/wiki/Skyrim:Dawnguard_Quests check the note section for each quest.

This is the second quest that I have had to use the console for advancing to the next stage. Prophet->Chasing Echoes.

Had this problem aswell. Thanks for the workaround Oltes.

Thank you, will give it a try:)

If your on the PC.. There may be an unofficial patch you can get.. But sometimes when I can't finish something due to bugs.. I use the console commands.. Riften in my game.. Had a lot of bugs..

Smack her.