The error could be the results of a number of configuration settings. I am including a couple of links which outline a number of class model names (including Duct) and field model names which could also be relevant.
Hopefully this will help to identify the underlying table requiring the model name.
Do you have the ArcFM Conduit Manager extension? If so you have a table called DuctDefinition which needs the model name DUCT assigned to it. This table has no relationships.
table DuctDefinition, model name DUCT
field Availability with field model name DUCTAVAILABILITY
field DuctID with DUCTID assigned
field DuctSize with DUCTSIZE assigned
If you cannot find it look for a feature class line or edge feature with the model name ULS assigned. In Minerville its called ConduitSystem and is the underground network edge. If you cannot find this I would do an ArcFM XML Export of just model names & see if any feature has DUCT or ULS model name assigned.