I came across this at work today. There was a problem when exporting Flash movies on an Apple Mac with the Actionscript 2.0 option checked.

The reason for this is that the AS2.0 Classpath has not been set. To correct this, when exporting select the "settings" and use the crosshair symbol under the title Classpath: to target the directory the classes are in.

The classes can be typically be found in : machd:Applications:Macromedia Flash 8:First Run:Classes:mx