CS3 to CS4 | ReferenceError: Error #1065: Variable is not defined

I have seen a few posts regarding: ReferenceError: Error #1065: Variable is not defined, but none solving this issue…

I have just upgraded to CS4 from CS3. I compiled and run the projects built in CS3 and get this error on loads of MovieClip classes available in the Library.

ReferenceError: Error #1065: Variable Movieclip_mc is not defined

Sounds like there is a difference in the compilers that is kicking this error up. I have tried creating a new central .fla document in CS4 and stil no good.

What’s going on here?