Type '{0}' cannot be added to list of known types since another type '{1}' with the same data contract name '{2}:{3}' is ...

Type '{0}' cannot be added to list of known types since another type '{1}' with the same data contract name '{2}:{3}' is already present. If there are different collections of a particular type - for example, List and Test[], they cannot both be added as known types.  Consider specifying only one of these types for addition to the known types list.