Java 1.6 applications are not allowed to redeploy in GAE / problem with Eclipse
Since February 2014, Google App Engine doesn't allow to redeploy applications compiled at Java 1.6 compliance level. Every project must be updated to Java 1.7 compliance level before (re)deployment. It may seem to be a simple task described here: https://developers.google.com/eclipse/docs/jdk_compliance, but i f you are using Eclipse you may experience problems. Looks like there is some problem to update compliance level using Eclipse plugin - not every GAE SDK version can be easily updated to 1.7 compliance level . From my experience update doesn't work with GAE SDK 1.7.0 ( notice: GAE SDK version - not Java 1.7 ) or lower. I haven't evaluated which GAE version is the lowest one that allows migration to Java 1.7, but I've figured out that it can be done using GAE 1.8.7 Problem with migration is probably related to GAE SDK / Eclipse plugin for GAE.