Error in slave Configure screen

I've configured the EC2 plugin to start spot instance m3.xlarge slaves in a VPC in us-east-1d, tagged with certain EC2 tags that I've specified, and the slaves connect back to the master via JNLP. When the slaves appear in the list of nodes, and I click on the Configure icon to configure them, the configure page renders up until the 'Tags' section then the rest of the page is replaced with a Jenkins error report. I've attached a screenshot and stack trace.