Cause
This error occurs if you attempt to add an object to a set and the object already exists in the set, or to a dictionary when an entry with the same key and object identifier (OID) already exists in the dictionary. Duplicate objects are not allowed in an automatically maintained member key dictionary, even if the dictionary allows duplicate keys. It is possible to add the same object more than once to a manually maintained dictionary if the object is added with different keys.
Action
Determine why an object is being added to the set or dictionary more than once and correct the code that led to the error. The method and source position containing the expression at which the exception was raised are reported in the error description.