I suspect what happend is that for some reason the cache was still locked (maybe from PK/aptdaemon) so the release upgrader exited after updateing the sources.list. That then triggered a "partial update" dialog and that the end of the partial upgrade in the cleanup phase it tried to get the remoal blacklist which is no longer on the system.
I suspect what happend is that for some reason the cache was still locked (maybe from PK/aptdaemon) so the release upgrader exited after updateing the sources.list. That then triggered a "partial update" dialog and that the end of the partial upgrade in the cleanup phase it tried to get the remoal blacklist which is no longer on the system.