It's seems as though I'm missing something incredibly obvious here. I have two glazed curtain walls that meet at a corner. I placed a corner mullion, and received the message following message:

"A Corner Mullion has been placed at the end of a Curtain Wall that is not joined to another Curtain Wall. The angle of the Corner Mullion will default to 90 degrees."

It's fine that the mullion is at 90 degrees, but I want to do this right. So how do you join two curtain walls? Thanks for your help.