Delete the change label before the import of the same label.
Or correct the inconsistency. You can check it with the following statement:
from DialogTag t
join DialogTaggedItem i on t.UID_DialogTag = i.UID_DialogTag
group by t.Ident_DialogTag,
order by 4 desc
The count should be "1" in every line.
If the combination of the change label and the tagged object exists more than once. it would indicate such an inconsistency.