title: Failed to create the part's controls in Eclipse with Salesforce
body: <p>I have Eclipse Juno and Force.com IDE. When I try to create new classes they always show: <strong>failed to create the part's controls</strong>. It worked for the first time, but now they always show this. Same happens if I create them inside the <code>force.com</code> platform. </p>
  
  <pre><code>Error details:
  org.eclipse.core.runtime.AssertionFailedException: assertion failed:
  at org.eclipse.core.runtime.Assert.isTrue(Assert.java:110)
  </code></pre>
  
  <p>etc ...</p>
  
  <p>I would appreciate all help.</p>