Besides the runtime error, you get Compiler Errors , correct your code as @recursivity:
function doubleSize(e:MouseEvent):void { e.currentTarget.scaleX=2; e.currentTarget.scaleY=2; }
Check the "Compiler Errors" tabs, and if you get them, you can largely ignore the further output and behavior that you get from your Flash.
EDIT: There is absolutely nothing wrong with choosing many different elements together, and then them (or "combining") in Symbol (MovieClip).
The reason you get ReferenceError runtime AFTER a compiler error (which is very strange) is because you are using TLF text fields , check this thread on the adobe forums for more information. My advice, for simplicity, is to switch to Classic Text text fields (there is a drop-down list selector on the TextField properties panel, the default TLF is on Flash CS5 +).
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