title: error running builder in GaeNature, Google App Engine in Eclipse
body: <p>I get an intermittent error when launching Eclipse with an open GAE project. It prevents me from building my project. I can sometimes get it to clear by deleting the contents of the "war/WEB-INF/classes" folder and then restarting Eclipse. Sometimes I close the project, close eclipse, launch eclipse, open the project and that seems to help.  The error has been happening for several months and has persisted through a GAE plugin upgrade. I can usually get Eclipse to work eventually. Once it works it keeps working great until I relaunch it.</p>
  
  <p>I am using GAE appengine-java-sdk-1.6.3
  GWT 2.4.0
  Objectify 3.1 (love it)
  Eclipse Indigo SR2
  Windows 7 64-bit</p>
  
  <p>It feels like maybe a race condition when starting Eclipse.</p>
  
  <p>Any ideas?</p>
  
  <p>These errors occur during the build ======================</p>
  
  <p>Errors running builder 'Java Builder' on project '<em>*</em>'.
  com/google/appengine/eclipse/core/nature/GaeNature</p>
  
  <p>Errors running builder 'Google WebApp Project Validator' on project '<em>*</em>'.
  java.lang.NullPointerException</p>
  
  <p>Error instantiating builder 'com.google.appengine.eclipse.core.projectValidator'.</p>
  
  <p>Plug-in com.google.appengine.eclipse.core was unable to load class com.google.appengine.eclipse.core.validators.GaeProjectValidator.</p>
  
  <p>An error occurred while automatically activating bundle com.google.appengine.eclipse.core (841).</p>
  
  <p>Plug-in com.google.appengine.eclipse.core was unable to load class com.google.appengine.eclipse.core.validators.GaeProjectValidator.</p>
  
  <p>An error occurred while automatically activating bundle com.google.appengine.eclipse.core (841).</p>
  
  <p>===================</p>
  
  <p>I also got this error when trying to open the Google/App Engine properties dialog in Eclipse </p>
  
  <p>Unable to create the selected property page.
  An error occurred while automatically activating bundle com.google.appengine.eclipse.core (841).</p>