Not sure if this is a coincidence, but yesterday when upgrading I performed the restore from a backup procedure. I encountered the same problems as seen in this thread.

This morning, I did the upgrade again but didn't perform a restore. All seems well now... and microb installed fine.

Not sure if there is a problem with the backup / restore procedure or if the repositories have been fixed? (am quite new to all of this so forgive me if i'm talking dross)