OnShutdown: COM object that has been separated from its underlying RCW cannot be used

Error Message

In some instances, when closing ArcMap, the following error message returns:

Error:   
"OnShutdown: COM object that has been separated from its underlying RCW cannot be used."

Cause

• ArcGIS for Desktop is referencing a previous version of an add-in. Add-ins are not backward compatible. For example, add-ins targeting ArcGIS for Desktop 10.3 do not work with earlier versions of ArcGIS for Desktop.
• Third-party extensions are installed on ArcGIS for Desktop. Even though third-party extensions can be installed on ArcGIS for Desktop, Esri does not support some extensions (thus, an error returns). 

Solution or Workaround

• Remove older versions of add-ins.

1. Navigate to C:\Users\<USERNAME>\Documents\ArcGIS\AddIns\Desktop10.x.

Note: 
Desktop10.x is used as a placeholder for versions of ArcGIS for Desktop. Replace the x in Desktop10.x according to the version installed on the target machine. 

2. Move all ArcGIS for Desktop folders older than the current version installed from the current location to another location on the computer.
3. Open and close ArcMap to test if the error message persists. 

Note: 
If the error message does not return, the folders that were moved can be deleted. However, if the error message persists, move the folders back to the original location. 

• Uninstall the problematic third-party extensions.