You can determine which control to be shown on top of others by setting a
proper z-index. The Default z-index for the RadGrid's PopUp edit form is 2500 and the RadMenu is 7000. In your case you can set the z-index for the PopUp edit form not lower than 7001, or set z-index for RadMenu which should be less than the z-index of the PopUp edit form. You can find more information about the
z-indexes here.