this happens , take a look (walls)....

[ntnik]

walls i'm trying to join are identical in every way (works fine on other corner) i even moved the basement wall down to avoid any conflict

[William Troeak]

By chance do you have the wall set to not allow join?

[saeborne]

I've noticed similar problems when a room separation line is co linear with a wall. Perhaps you have this condition?

[saeborne]

Another thing that usually irons out wall join conditions...

I split each wall back about 4' from the corner.
Delete the new 4' wall lengths.
Then do a Trim command back on the remaining walls.

Perhaps this will help you?

[josh.made4worship]

I have this problem a lot and I am never really sure why it happens. It seems like you'll clean up the wall and then the next day or later you have the same problem again.

Usually, what I do to fix it, is to select one of the walls and click on the blue grip...a lot of times it will re-clean itself up. Sometimes, you have to tinker a little further, like pulling the wall apart and re-triming or something.

Hope that helps.