Chances are you probably have the wrong "object" selected. be sure the "Objects Docker" is visible and selected. It should appear on the left-hand side of the screen, just left of the Color Pallete. If there is no tab that says "Objects" or it is not visible go to Window -> Docker -> Objects (or CTRL+F7). This shows you all the objects in your layout. Chances are you have the wrong object selected, or you are cloning from the proper object, and trying to paint the cloned item on to a different object (or no object at all). Use the pick tool to click on the object you want to clone, it should show up in the objects window with the red box around the thumbnail. Be sure that there is ample "canvas" to clone the new area to. If not, it may clone to an underlying object, or may not clone at all if the object is to small. Hope that gets you pointed in the right direction.