Google App Engine NO_MODIFICATION_ALLOWED_ERR Eclipse build error

Question

I have installed Google App Engine plugin for Eclipse Indigo. I have created new Web Application Project with auto generated sample code. I unchecked "use Google Web Toolkit" when creating a project. My project looks as described here: Google App Engine HTTP Error 403

When building the project, I get the following error:

Errors occurred during the build.

Errors running builder 'Google App Engine Project Change Notifier' on project 'Test

NO_MODIFICATION_ALLOWED_ERR: An attempt is made to modify an object where modifications are not allowed.

I can run the servlet on the localhost, without any problems, however when I deploy the application, it doesn't work. Logs show:

Uncaught exception from servlet

java.lang.UnsupportedClassVersionError: test/Test : Unsupported major.minor version 51.0

Answer 1

The problem was caused by Java 7. Google App Engine supports Java 6 only.