This issue occurs when a constituent has multiple spouses (a problem that can occur during data conversion). To determine which constituent records have multiple spouses, run the following SQL query:
select RELATIONSHIPCONSTITUENTID, CONSTITUENT.NAME, COUNT(*)
inner join dbo.CONSTITUENT
on CONSTITUENT.ID = RELATIONSHIPCONSTITUENTID
where ISSPOUSE = 1
group by RELATIONSHIPCONSTITUENTID, CONSTITUENT.NAME
having COUNT(*) > 1
This problem can be resolved by deleting the duplicate spouse records from the database.