But did it save?
mostly this message pops up if you have component’s downloaded from the 3D Warehouse,is this the case ?
If you open outliner , you can investigate these components for double wrapped instances, mostly , they’ll have the same name in the lower levels of the components . try exploding the first level. (inoutliner select highest level , rightclick->explode
(2) Try (View > Hidden Geometry) then selecting all (Edit > Select All)
Copy (Edit > Copy) open a new instance of SketchUp, and paste into the new empty model. (Edit > Paste)