When connecting to Jenkins 1.459 or later using the builds view or the automatic workspace provisioning provided with the HP ALM connector, you may see an error "Server validation failed: Unexpected error: null". Note that this is still an issue with Jenkins 1.466. This is not a bug in the connector but likely caused by the following Jenkins bug:
Content is returned for HEAD requests when using gzip
There will be a workaround in the latest EA version of Tasktop Dev and Mylyn. If you cannot update Tasktop Dev or Mylyn you will either have to wait until there is a new version of the software that you can update, downgrade your Jenkins server to the 1.447.1 release or wait until the issue is fixed in Jenkins and upgrade to that version.