Default Tray no longer working

The Default Tray is no longer available for selection in Sketchup. The Tray is open, and can be seen on the screen, but I no longer am able to select any tool, etc that is on it.

Problem has been resolved!
Issue was with in View / Toolbars / Options; the Show Screen Tips on Toolbar box was checked. Once this option is unselected the issue was resolved.