After jumping down the well returning the skeleton key and talking to nocturnal, i am unable to complete the mission as Karliah replies only "Yes fellow nightingale?". Luckily i saved before jumping down the well but it is still an inconvenience being unable to complete this mission. I've read on multiple forums about this problem happening to many other gamers. I have also read on several websites that on occasions karliah mysteriously disappears, or is busy whenever the player tries to interact with her. I was hoping you'd look into patching this bug, or at least providing a solution to it. Thankyou very much.

P.s I think skyrim is one of the best game ever made. shame that it has this bug...

This seems to be caused by completing Hard Answers a second time.

• ⁽¹⁾ It helps to wait for a few hours after inserting the key. The game will reload upon completion of the wait with Karliah where she needs to be.

WARNING:

Do not complete the quest (HARD ANSWERS) a second time. Doing so will break the end of the "Darkness Returns" quest.

Karliah will not let you out of the last room and will only say "Yes, fellow Nightingale?" when spoken to. You will be stuck in that room permanently.

The only fix for this is to reload a save from before you started this quest a second time.* !!!

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* However, try first the solution above ⁽¹⁾

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So, know you have your solution !!!! Good Luck, and Happy New Year...

hail companion. Unfortunately it seems i have done hard answers a second time and have no game saves prior to this. Waiting doesn't seem to be working either. I have a level 71 character and i'm afraid restarting is out of the question due to the 500+ hours spent on the game. Does bethesda know about this problem and if so are they working on a patch?

No my friend, the latest patch is the 1.9 - there will be, no more patches. (at least for the console versions)

Skyrim PC, get unofficial patches even those days. !!!