I've got TortoiseBazaar installed on my Windows laptop, and I was trying to branch a repository hosted on my VPS to another directory on my VPS, and I got this lovely error:

bzr: ERROR: Unknown branch format: 'Bazaar Branch Format 7 (needs bzr 1.6)

That lead me to this mailing-list archive: http://osdir.com/ml/bazaar/2009-06/msg00692.html

Then I tried following the instructions here to add the Launchpad PPA to /etc/apt/sources.list, but they forgot to mention that you need to do this:

sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com D702BF6B8C6C1EFD

Which I found out about here after I got this error:

GPG error: http://ppa.launchpad.net hardy Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY D702BF6B8C6C1EFD

after modifying my /etc/apt/sources.list and running:

sudo apt-get update

Just thought I'd save someone else some pain.

And of course, don't forget to uninstall the version of bzr that wouldn't play ball in the first place.