This almost certainly means you've had either a disk corruption error, or a machine crash right after doing a bzr command.
For the former, checkdisk sometimes finds and fixes things - we had a case of that recently on the bzr list.
For the latter problem, you may have the old pack files on disk still in obsolete_packs - if you do we might be able to manually move them back into place (but don't just do it - its going to need some python etc).
This almost certainly means you've had either a disk corruption error, or a machine crash right after doing a bzr command.
For the former, checkdisk sometimes finds and fixes things - we had a case of that recently on the bzr list.
For the latter problem, you may have the old pack files on disk still in obsolete_packs - if you do we might be able to manually move them back into place (but don't just do it - its going to need some python etc).
-Rob