Unable to unlock the anti-theft system using remote and/or master key in my 1994 600SL--any suggestions? Anyway to bypass anti-theft system when it goes haywire? Thanks.

Try pulling the fuse to the alarm system. I don't know where the fuse is on a coupe, but on a sedan, I think it's in the trunk. The starter interrupt should "fail safe", meaning it takes the alarm being activated (tripped) to prevent the engine from cranking, so pulling the fuse should allow you to start the car.