Does this happen with every SKP you try, or a specific SKP that might be corrupted ?
If it's SKP related try this.
Open a new SKP.
Preferences > General > Check models for problems tick Automatically check... AND Automatically fix...
OK.
Close SketchUp.
Now reopen the problem SKP.
It should be fixed as SketchUp opens it.
Now try Model Info... again...
If it occurs with every SKP then you need to use Control Panels > Programs and Features and Reinstall/Repair SketchUp v2013 - something is wrong and needs fixing.
Failing that, try uninstalling SketchUp and reinstalling from scratch...
Any custom files you have [e.g. Plugins will NOT be deleted by a proper uninstall using the system-uninstaller]