title: Debugging JDO error
body: <p>My application is throwing this error:</p>
  
  <pre><code>Error : An error occurred trying to instantiate an instance of the API adapter "org.datanucleus.api.jdo.JDOAdapter" 
  (perhaps you dont have the requisite datanucleus-api-XXX jar in the CLASSPATH?) : 
  {1}
  org.datanucleus.exceptions.NucleusUserException: Error : 
  An error occurred trying to instantiate an instance of the API adapter "org.datanucleus.api.jdo.JDOAdapter" (perhaps you dont have the requisite datanucleus-api-XXX jar in the CLASSPATH?) : 
  {1}
  ...
  at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)
  </code></pre>
  
  <p>Although my application do have <code>datanucleus-api-jdo-3.0.0-release.jar</code></p>
  
  <p>What could be the reason if not missing jars?</p>
  
  <p>EDIT:</p>
  
  <p>This is what have been suggested to fix this issue:</p>
  
  <blockquote>
    <p>This is a sporadic error that happens from time to time on any
    persistable class, but moreso on ones that are used a lot in parallel.
    It happens in JDO and JPA, and it seems as though the local datastore
    locks a particular table / entity group and forgets to release it;
    thus causing all subsequent calls to ds operations to fail. I
    generally don't have to restart eclipse; just stopping then starting
    the server tends to fix the problem, if not, a full refresh/clean
    build will do the trick.</p>
  </blockquote>
  
  <p>However, I have already restarted my GAE server and re-run my application still getting the same error.</p>
  
  <p><strong>Here is the complete</strong> <a href="http://pastebin.com/JAbwXjHA" rel="nofollow">POM.xml</a></p>
  
  <p><strong>Here is the complete</strong> <a href="http://pastebin.com/1Rm7UUF0" rel="nofollow">stack trace.</a></p>