When I adda a class to my work why I am getting 1046: Type was not found Error?

Hi everyboy,

My work normally Works fine. But I decided to add a class (controlParts.as). Although this class empty (includes the default creation includings), my work gives an error:
1046: Type was not found or was not a compile-time constant: IOErrorEvent.
I didnt add anything to the class. It is emty. Why I am getting error like missing import elements?