Transmission Screen Problems

[Malibu Jim]

Since I've recently puchased 5 qts of Nissan Matic D, transmission pan gasket & screen, I figured I'd replace these for the first time in my 2002 I35. After draining the fluid and dropping the pan, I loosen the 12 bolts retaining the screen and BINGO, the lone stud with the nut is turning.! Must have a nut on the other end, as it didn't back out. Any suggestions for next time? Maybe try to hold the stud with vicegrips or grind a slot in the bottom for a straight bladed screwdriver ??? I assume there's no way to get to the other end of the stud, with the transmission in the car. Why 13 fasteners to hold the screen ???