Okay so I've been having a little bit of trouble with the quest Discerning the Transmundane. So I've transcribed the Lexicon and I go to bring it back to Septimus and he talks and then continues to give the second half of the quest in which I have to acquire the blood and as I'm trying to leave his place the Wretched Abyss is blocking my path. I press 'A' to attempt to speak with it and no results. I've reloaded a few times to different spots and it continues to occur. Do I have to wait for a courier to deliver me a letter from Septimus summoning me to his place then get the second half of the quest or am I just screwed on this? Any help would be greatly appreciated. P.S. I am above the level of 15, I'm 17.
Try loading a save prior to entering Septimus' outpost. Hermaues Mora should automatically attempt to speak with you when you approach so there's obviously a bug
re-load your save but instead of continuing with the quest get out and do something else, maybe do another quest and then come back to him later. give that a go, should be working cause iv had the same problem as you and that's what iv done if glitches like that accrue.