title: Eclipse Juno build error with "Maven Project Builder"
body: <p>When I try to clean &amp; build my Maven project I get the following error:</p>
  
  <pre><code>Errors occurred during the build.
  Errors running builder 'Maven Project Builder' on project '(Hid Project Name)'.
  org/apache/maven/project/MavenProject
  Errors running builder 'Maven Project Builder' on project '(Hid Project Name)'.
  org/apache/maven/project/MavenProject
  </code></pre>
  
  <p>similarly with the clean all process, it throws the following:</p>
  
  <pre><code>Errors occurred during the build.
  Errors running builder 'Maven Project Builder' on project '(Hid Project Name)'.
  loader constraint violation: loader (instance of org/eclipse/osgi/internal/baseadaptor/DefaultClassLoader) previously initiated loading for a different type with name "org/apache/maven/plugin/MojoExecution"
  Errors running builder 'Maven Project Builder' on project '(Hid Project Name)'.
  org/apache/maven/plugin/MojoExecution
  Errors running builder 'Maven Project Builder' on project '(Hid Project Name)'.
  org/apache/maven/plugin/MojoExecution
  Errors running builder 'Maven Project Builder' on project '(Hid Project Name)'.
  org/apache/maven/plugin/MojoExecution
  Errors running builder 'Maven Project Builder' on project '(Hid Project Name)'.
  org/apache/maven/plugin/MojoExecution
  Errors running builder 'Maven Project Builder' on project '(Hid Project Name)'.
  org/apache/maven/plugin/MojoExecution
  Errors running builder 'Maven Project Builder' on project '(Hid Project Name)'.
  org/apache/maven/plugin/MojoExecution
  Errors running builder 'Maven Project Builder' on project '(Hid Project Name)'.
  org/apache/maven/plugin/MojoExecution
  Errors running builder 'Maven Project Builder' on project '(Hid Project Name)'.
  org/apache/maven/plugin/MojoExecution
  Errors running builder 'Maven Project Builder' on project '(Hid Project Name)'.
  org/apache/maven/plugin/MojoExecution
  Errors running builder 'Maven Project Builder' on project '(Hid Project Name)'.
  org/apache/maven/plugin/MojoExecution
  </code></pre>
  
  <p>Any ideas what causes this?</p>