If tableField = "Process ID" and layerField = "PID" then this works:
IRelationshipClass relationshipClass =
memoryRelationshipFactory.Open(
"Join",
table as IObjectClass,
tableField,
geoFeatureLayer.DisplayFeatureClass as IObjectClass,
layerField,
"forward",
"backward",
esriRelCardinality.esriRelCardinalityOneToOne );
If tableField = "Process ID, Year Made" and layerField = "PID, YM" then it fails.
(Table is SQL Server table.)
I have tried brackets and quotes to no effect. Is it possible to pass a compound key?