I also want to say ceiling light, those are often the culprit.
Have you tried the "go here" interaction on the other side of the door? The door itself may not actually be blocked. I've sometimes ran into sims doing this because the place they're going to is blocked, or the patching to get there and use that object is too complex. Whereas a "go here" in front of the object they have to use works fine. As in "from my current position in the upstairs bathroom I can see that I won't be able to use the TV in the man cave in the basement. But I can get to the basement just fine and use the tv after I get there."
Don't ask me why the game is like this, but it's just something I've run into a few times