So you got to Meridia and picked up the "Vale of Twilight" chain from the NPC by the mailbox.
Then you spend god knows how long getting your five Shavarath Stone of <Whatever>, and have returned to Meridia to finish this quest.
What's that? You didn't have the stones in your actual inventory (as opposed to inside a bag in inventory) and went to the Eldritch Chamber and made your Shavarath Signet Stone without advancing the quest?
Guess what? You're screwed. Unfortunately it wasn't me that this happened to.
Make absolutely sure that your quest chain advances before making the signet stone!
This has been your friendly neighborhood metalhead's warning of the day. Please comply... Or we'll grind you into food for the rest of us!
I put in a bug report for this already. As I believe you should be forbidden from making the signet stone before the chain advances, and got a pm from Cotoci saying they received it. Let this serve as a warning for everyone.