When I get too the the vacant floor glyph Karliah is gone does and does not open the door. I play on PC. It has been too long for me too reload (I leveled like 8 times since I started too care :P) I thought Karliah would apear and everything would be fine but she didn't help please!
I had the same problem just now trying to work my way through it. Instead of opening the door she just...left. I decided to follow her after the third time, having reloaded a handful of previous saves, and a little over halfway to Windhelm I gave up. I tried attacking her, but she didn't turn around, so I found a console command that would complete that part of the quest for me...the problem was, then Bryn ended up stuck inside the gate even though Karliah hadn't opened it. Ugh. I teleported them both to me and now they won't leave me alone.