I saw this question asked several times, therefore I think a short blog entry might help in solving a common e4 launch problem.
If you run e4 you need to include the declaritive service implementation into your launch config. If you don’t you currently receive the following NPE:
java.lang.NullPointerException at org.eclipse.e4.ui.internal.workbench.E4CommandProcessor.processCommands(E4CommandProcessor.java:52)
If you face such an error, make sure org.eclipse.equinox.ds and org.eclipse.equinox.util are included in the launch config.
I hope that at some point a better error message will be issued. Please see Bug 318821 for details.