Attempting to upgrade from 1.409.1 to 1.409.2 failed: Jenkins reported that an update was available but due to a server-side issue, it was then unable to actually download the new .war file.
Since then, Jenkins only displays:
with no way to re-try the upgrade process (now that the issue on the server has been resolved). Also see attached screenshots.
Adding a simple "retry" button would help here.
For more context, see http://groups.google.com/group/jenkinsci-dev/browse_thread/thread/5fdd91ec3c4080d0