I took the first Totems of Hircine quest from Aela (the one where you have to retrieve the first Werewolf Totem from the egg sac at the bottom of the spider-infested cave). This all went off without a hitch, but now I'm back in Whiterun and I cannot open the door to the Underforge. The quest marker shows up on it, but I do not get the option to activate / open it when I get near it. Aela only says that "Now is not the time for talking, we need to get to the Underforge and see what this thing does" or somesuch.

Note that I am personally no longer a werewolf -- I turned myself back after I had finished "curing" the two brothers. So maybe I can't get into the Underforge because I'm no longer a werewolf? But if that were the case, why should I have been able to flag this quest in the first place (if there's no way to finish it)? Right now I seem to be stuck with Aela as a permanent companion, with no apparent way to complete this quest. Anybody else have this issue?

Just to follow up on my own post, I made this go away by entering "setstage CR12 100" from the console. This made Aela go into the Underforge (I wasn't able to follow her). I haven't done any more Companions quests (I'm already the Harbinger) but this does seem like something that might need a bit of tweaking / debugging.

Just to confirm, you are correct that it is because you cured yourself. Once you do that you lose access to the underforge. Hopefully in a future patch they will remove the totem quests if you remove your beast form.