This is a fairly common problem that newbies using Google Web Kit within Eclipse encounter with their the Java Runtime Environment. Chances are you just upgraded your JRE to 1.6.0_31.

The solution is to add an extra parameter in your virtual machine run configuration using either:

-Dappengine.user.timezone=UTC

If that does not work, try this.

-Dappengine.user.timezone.impl=UTC

To go to the run configuration, do the following:

1. Right click project name
2. Go to Run As > Run Configurations
3. Go to Arguments tab
4. Under VM Arguments, add the extra parameter, then click Run button

There you go! That should get you back into development mode!