raise an ValueError with an argument string "'%s.%s' has more than one ForeignKey to '%s.%s'.", where '%s' is replaced with,
raise ValueError ( "'%s.%s' has more than one ForeignKey to '%s.%s'." % ( model . _meta . app_label , model . _meta . object_name , parent_model . _meta . app_label , parent_model . _meta . object_name ) )