'toplevel.as' could not be found

I have re-installed 2004 MX. I have a very simple dynamic masking application. [COLOR=Navy]mask_mc.onEnterFrame = function() {
this._x = _root._xmouse;
this._y = _root._ymouse;
};
maskedbg_mc.setMask(mask_mc);[/COLOR]

[COLOR=Black]It works. BUT I get this error message.
[COLOR=Red]
Warning Scene=Scene 1, layer=action, frame=1:Line 1: The file ‘toplevel.as’, which is required for typechecking ActionScript 2.0, could not be found. Please make sure the directory ‘$(LocalData)/Classes’ is listed in the global classpath of the ActionScript Preferences.
mask_mc.onEnterFrame = function() {

Total ActionScript Errors: 1 Reported Errors: 1[/COLOR]

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