I encountered this error when deploying a Google AppEgine app:
Java 6 applications cannot be deployed to Google App Engine from any version of the SDK… you can request that your application be whitelisted for Java 6 deployment from http://goo.gl/ycffXq.
And so I have to add Java 7 SDK to Eclipse.
This is what you have to do:
Download & install Java 7 JDK
In Eclipse, go to Preferences > Java > Installed JREs > Add, then select the directory, which should be
Tick the checkbox to make Java SE 7 the default
Go to Preferences > Java > Compiler > Compliance Level > Select 1.7
Test, and deploy!
There should not be any problem with migrating to Java 7.