We really didn't have a crisis leading up to the wedding, not that I can imagine.
My best wedding-day crisis, though: I was an usher in a friend's wedding that was in an old and tiny historic church on Long Island in the middle of the summer. It was beastly hot in there, so everyone was hanging out outside until we went out and said "We want to start now, everyone come sit down." And then everyone came in at once, faster than the three of us could seat them, so people were seating themselves.
The pews on each side held three or four people. The first pew on the bride's side was reserved for the bride, groom, and maid of honor to sit down at one point in the service. Second pew: bride's mother, her husband, and the bride's brother. Third pew: bride's father, his wife and someone else from their entourage. Bride's mom and dad do not get along. So amid the stampede, we notice three women we didn't recognize sitting in the second pew on the bride's side. The bride's mom noticed this too and was standing at the back of the church looking furious. The ushers conferred, and I went up and asked "Who are you?" They said "[The bride's father] said we could sit here."
The ushers conferred, and we cleared out a pew in the far back of the church that was stacked with hymnals and bibles. I went back to them and said "You're going to have to sit back there. I don't care what he said, I'm not telling the mother of the bride that she has to sit in the back of the church." They were pissed, but fuck 'em.
The bride and groom were blissfully unaware of this minor drama until I told them several years later. Then they were grateful.