You are trying to manipulate a coded value domain; however, a domain of this type does not exist in the workspace you have specified.
Before using the Add Coded Value To Domain or the Delete Domain tools, your database must contain a coded value domain. Verify that the domain you are trying to manipulate is of type coded value. For more information on domains, see An overview of attribute domains. For more information on the geoprocessing tools that manipulate domains, see An overview of the Domains toolset.