@zookyman2 - the reason why is that is cause, he said "You Open a New Document, And Make Sure, You Selected "ActionScript 2.0" instead of "Actionscript 3.0" while making a new document.
Just Press Ctrl+N or Click File > New. Now Make Sure ActionScript 3.0 is not selected and ActionScript 2.0 is selected. if not, Select ActionScript 2.0. If ActionScript 2.0 is already selected, leave it and click OK. Now Try adding actionscript to your button and it will work :)