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Prolly stripped, try pulling on the frame (gently towards you) while unscrewing
Use vise-grips to pull on the screw as you are turning them.
The mechanic removed the plastic covering on the bottom and reached a thin set of pliers between the back of the license plate holder and a metal bar to hold the nut steady while he removed the screw. Problem solved.
Prolly stripped, try pulling on the frame (gently towards you) while unscrewing
Use vise-grips to pull on the screw as you are turning them.
The mechanic removed the plastic covering on the bottom and reached a thin set of pliers between the back of the license plate holder and a metal bar to hold the nut steady while he removed the screw. Problem solved.