I updated to the latest app engine version 1.8.4 and the latest Eclipse plugin for app engine. I am using Eclipse version: 

Eclipse Standard/SDK

Version: Kepler Release

Build id: 20130614-0229

Google App Engine Java SDK 1.8.4 1.8.4 com.google.appengine.eclipse.sdkbundle.feature.feature.group Google, Inc.

Google Plugin for Eclipse 4.2 3.4.0.v201309051717-rel-r42 com.google.gdt.eclipse.suite.e42.feature.feature.group Google, Inc.

When I try to launch my project I get this error. If I switch back to 1.8.1 it works fine. I am using Google Cloud Endpoints, but otherwise nothing too exotic, no Spring, etc.

Thanks for the help!