When Hudson is restarted after configuring an EC2 cloud, the attached error shows up in Hudson's log, and the cloud configuration is no longer present. Also see http://hudson.361315.n4.nabble.com/Initialization-error-with-EC2-plugin-td2173614.html. I got this error when running via hpi:run on trunk (ec2 plugin 1.9-SNAPSHOT) but we're also seeing it with the released 1.8 on ci.hudson-labs.org.