Cause
This error occurs if your application code attempts to assign a value to a member key dictionary at a specified key.
By definition, the elements of a member key dictionary are automatically keyed using one of the properties of the element, so you cannot supply an external key with the element. Instead, the
Action
Change your application code to use the add method to add the element to the dictionary. If you want to use an external key to access the element, you may need to redefine the dictionary to be an external key dictionary.