Quoted from dsuperbee:Use a dremel and cut off the top of the screw so it is able to drop through the hole.
Definitely do this if you are able. If the nut is to close to the playfield or you dont have the tools then you need to start trying products to unbind the threads. I had a similar issue with a t-nut and screw on my mpf. I used penetrating oil. Apply in small amounts so that you only get it on the t-nut and screw. Give it time to soak in and add some more.