We wonder why there is the need to run bzr switch.
This will not work if you checkout anonymously a branch from Launchpad, eg. lp:openpetraorg.

It works for the first build and checkout:

from the log:
$ bzr checkout --lightweight lp:openpetraorg "C:\Program Files (x86)\Jenkins\workspace\OpenPetraBuildWinTimotheus"
You have not informed bzr of your Launchpad ID, and you must do this to
write to Launchpad or access private data. See "bzr help launchpad-login".
Getting local revision...
$ bzr revision-info -d "C:\Program Files (x86)\Jenkins\workspace\OpenPetraBuildWinTimotheus"
info result: bzr revision-info -d C:\Program Files (x86)\Jenkins\workspace\OpenPetraBuildWinTimotheus returned 0. Command output: "2226 timotheus.pokorra@solidcharity.com-20130515153627-dvnp06rop5rtzcfa
" stderr: ""
RevisionState revno:2226 revid:timotheus.pokorra@solidcharity.com-20130515153627-dvnp06rop5rtzcfa
No emails were triggered.

and builds fine.

The second build, no change on the code, same revision 2226:

$ bzr revision-info -d "C:\Program Files (x86)\Jenkins\workspace\OpenPetraBuildWinTimotheus"
info result: bzr revision-info -d C:\Program Files (x86)\Jenkins\workspace\OpenPetraBuildWinTimotheus returned 0. Command output: "2226 timotheus.pokorra@solidcharity.com-20130515153627-dvnp06rop5rtzcfa
" stderr: ""
[OpenPetraBuildWinTimotheus] $ bzr update
Tree is up to date at revision 2226 of branch http://bazaar.launchpad.net/~openpetracore/openpetraorg/trunkhosted
[OpenPetraBuildWinTimotheus] $ bzr switch lp:openpetraorg
bzr: ERROR: Cannot lock LockDir(http://bazaar.launchpad.net/~openpetracore/openpetraorg/trunkhosted/.bzr/branch/lock): Transport operation not possible: http does not support mkdir()
ERROR: Failed to switch
Since BZR itself isn't crash safe, we'll clean the workspace so that on the next try we'll do a clean pull...

But then it does not recover from that, and the build fails.