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(*)
from relationship
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.