title: GWT/ Eclipse: ClassNotFoundException com/google/gwt/dev/Compiler
body: <p>i recently updated from GWT 2.0.4 to 2.1.0. Since then I cannot compile my GWT application anymore. When I click on the GWT compile button of the GWT eclipse plugin I get the following error: </p>
  
  <pre><code>java.lang.NoClassDefFoundError: com/google/gwt/dev/Compiler
  Caused by: java.lang.ClassNotFoundException: com.google.gwt.dev.Compiler
   at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
   at java.security.AccessController.doPrivileged(Native Method)
   at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
   at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
   at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
   at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
  Exception in thread "main"
  </code></pre>
  
  <p>Also I can't create a new GWT project in Eclipse. In the new New Web Application Project Dialog one can choose to use GWT and/or Google App Engine. When check "Use GWT" a error dialog raises up which says:
  "Creation of element failed. Reason: Invocation of com.google.gwt.user.tools.WebAppCreator failed. See the error log for more details."</p>
  
  <p>In the log file (<code>&lt;workspace&gt;/.metadata/.log</code>) I can see the message: </p>
  
  <pre><code>!ENTRY org.eclipse.jdt.ui 4 10001 2010-11-02 08:34:50.085
  !MESSAGE Internal Error
  !STACK 1
  Java Model Exception: Core Exception [code 0] Invocation of com.google.gwt.user.tools.WebAppCreator failed. See the error log for more details.
   at org.eclipse.jdt.internal.core.BatchOperation.executeOperation(BatchOperation.java:50)
   at org.eclipse.jdt.internal.core.JavaModelOperation.run(JavaModelOperation.java:728)
   at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:1975)
   at org.eclipse.jdt.core.JavaCore.run(JavaCore.java:4777)
   at org.eclipse.jdt.internal.ui.actions.WorkbenchRunnableAdapter.run(WorkbenchRunnableAdapter.java:106)
   at org.eclipse.jface.operation.ModalContext$ModalContextThread.run(ModalContext.java:121)
  Caused by: org.eclipse.core.runtime.CoreException: Invocation of com.google.gwt.user.tools.WebAppCreator failed. See the error log for more details.
   at com.google.gwt.eclipse.core.runtime.tools.WebAppProjectCreatorRunner.createProject(WebAppProjectCreatorRunner.java:53)
   at com.google.gdt.eclipse.suite.wizards.WebAppProjectCreator.createGWTProject(WebAppProjectCreator.java:532)
   at com.google.gdt.eclipse.suite.wizards.WebAppProjectCreator.create(WebAppProjectCreator.java:294)
   at com.google.gdt.eclipse.suite.wizards.NewWebAppProjectWizard.finishPage(NewWebAppProjectWizard.java:147)
   at org.eclipse.jdt.internal.ui.wizards.NewElementWizard$2.run(NewElementWizard.java:117)
   at org.eclipse.jdt.internal.core.BatchOperation.executeOperation(BatchOperation.java:39)
   at org.eclipse.jdt.internal.core.JavaModelOperation.run(JavaModelOperation.java:728)
   at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:1975)
   at org.eclipse.jdt.core.JavaCore.run(JavaCore.java:4777)
   at org.eclipse.jdt.internal.ui.actions.WorkbenchRunnableAdapter.run(WorkbenchRunnableAdapter.java:106)
   at org.eclipse.jface.operation.ModalContext$ModalContextThread.run(ModalContext.java:121)
  !SUBENTRY 1 com.google.gwt.eclipse.core 4 0 2010-11-02 08:34:50.085
  !MESSAGE Invocation of com.google.gwt.user.tools.WebAppCreator failed. See the error log for more details.
  </code></pre>
  
  <p>gwt-dev.jar, gwt-user.jar and many other google-jars are in the classpath...</p>
  
  <p>Does anyone have an idea how to solve this issue? 
  I also set up a new fresh Eclipse installation, installed the new GWT plugin, and chose a new workspace directory, but this still gives me the errors...</p>
  
  <p>Additional information: </p>
  
  <ul>
  <li>Windows XP,  </li>
  <li>Eclipse for Java EE 3.6 Helios,  </li>
  <li>J2EE / Java 1.6.0_22-b04</li>
  <li>Google Plugin for Eclipse 3.6  1.4.0.v201010280102,</li>
  <li>Google App Engine Java SDK 1.3.8  1.3.8.v201010161055 </li>
  <li>Google Web Toolkit SDK 2.1.0  2.1.0.v201010280102</li>
  </ul>