I am having trouble advancing in the skyrim quest Discerning the transmundane. I give the lexicon to Septimus, and he tells me to the harvest elf blood. I then try to leave the outpost, but the wretched abyss is in my way and it won't respond when I try to talk to it. I know some daedra is supposed to talk to me after I get the elf blood extractor, but that hasn't happened. I tried downloading Dawnguard in hopes to fix the problem, but that hasn't worked. I am wondering if I should try a different Skyrim disc, because this bug is driving me nuts. Any of you have any suggestions? Any help would be much appreciated.
It sounds to me like one of the characters isn't following their script correctly here. Although I've yet to hear about this quest bugging out. You may have done something before giving Septimus the lexicon that bugged one of the character scripts.
The best advice is reloading a previous save, even reloading the auto-save right before entering this area should reset the script for you.