I am having RadToolBar on my page which contains RADMenu.
And after expanding menu it goes behind DataGrid(InterSoft) placed on my page. EnableOverlay propertry of RadMenu is not working.
Try setting higher z-index value for RadMenu and see whether it helps. Add style="z-index:<some value>" to RadMenu in order to change the value. Also checkout the following documentation for z-index values for RadControls. Controlling absolute positioning with z-index