AppEngine SDK plugin installation killing my eclipse

[Sensi]

Hi @ll!

I've try to install the AppEngine SDK plugin for eclipse. But after
the restart of my eclipse I get an error message like this: An error
has occurred. See the log file /path/...

The logfile contains following content:

!SESSION Fri May 28 07:12:55 CEST 2010
-----------------------------------------
!ENTRY org.eclipse.equinox.launcher 4 0 2010-05-28 07:12:55.031
!MESSAGE Exception launching the Eclipse Platform:
!STACK
java.lang.ClassNotFoundException:
org.eclipse.core.runtime.adaptor.EclipseStarter
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:556)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:514)
at org.eclipse.equinox.launcher.Main.run(Main.java:1311)

I'm using Eclipse (JEE package, Galileo) on Mac Os X and using java
version "1.6.0_20" Java(TM) SE Runtime Environment (build 1.6.0_20-
b02-279-10M3065)

I feel really angry about that bug because my eclipse installation is
broken. I can't run eclipse anymore. If I try to delete all files
which were created at the plugininstallation, it doesn't have any
effect. I get the same errormessage like before.

Does everyone have the same problem with the sdk plugin and how to fix
it?

King regards
Michael Ofner