Error #1034: Type Coercion failed: DragManagerImpl to IDragManager

My Flex application is divided in modules, and I am having an advanced data grid in one of them.
While clicking on the advanced data grid, I am getting following error:

TypeError: Error #1034: Type Coercion failed: cannot convert mx.managers::DragManagerImpl@1ae729c1 to mx.managers.IDragManager.
    at mx.managers::DragManager$/get impl()[E:\dev\4.y\frameworks\projects\framework\src\mx\managers\DragManager.as:202]
    at mx.managers::DragManager$/get isDragging()[E:\dev\4.y\frameworks\projects\framework\src\mx\managers\DragManager.as:242]
    at mx.controls.listClasses::AdvancedListBase/dragScroll()[E:\dev\4.y\frameworks\projects\advancedgrids\src\mx\controls\listClasses\AdvancedListBase.as:6821]
    at Function/http://adobe.com/AS3/2006/builtin::apply()
    at SetIntervalTimer/onTimer()
    at flash.utils::Timer/_timerDispatch()
    at flash.utils::Timer/tick()

I fixed it by adding creating an instance of IDragManager in my main application class:

<fx:Script>
    <![CDATA[
        import mx.managers.IDragManager;
        private var iDragManager:IDragManager;
    ]]>
</fx:Script>