Data value named 'item' not found (Error 327)

The specified data value could not be found. This error has the following cause and solution:

• In the ReadProperties event of a UserDocument or UserControl, you passed in the name of a property to PropBag.ReadProperty that doesn't exist and you didn't specify a default value.

  To avoid this error, verify that the specified property exists or use the optional default parameter for the PropBag.ReadProperty.