Manual top on 96 Z3 will not close

This may sound obvious, but make sure the clamps are out of the way before trying to drop the pins into the holes.

Also, try tilting the front part of the top forward BEFORE the top is in it’s resting position (In other words, while it’s still a bit in the air above the car. I have a hardtop on, so I can’t go look at mine, but I also suggest comparing sides, to see if there is something out of place in the hinges and cables.