See http://musicbrainz.org/edit/17805486 - I don't have more details but that looks wrong.
Same issue http://musicbrainz.org/edit/17805473 - it might be related to removing a label that later got merged.
Both of these are removing a label that no longer exists; it's just not displaying. I'll whip up a patch to display the old label's name at the time of the edit when it can't load the actual label. Would that be sufficient, you think?