title: Py4JError: SparkConf does not exist in the JVM
body: <p>I am running pyspark but it can be unstable at times. There are couple of times it crashes at this command</p>
  
  <pre><code>spark_conf = SparkConf()
  </code></pre>
  
  <p>with the following error message</p>
  
  <pre><code>     File "/home/user1/spark/spark-1.5.1-bin-hadoop2.6/python/pyspark/conf.py", line 106, in __init__
  self._jconf = _jvm.SparkConf(loadDefaults)
       File "/home/user1/spark/spark-1.5.1-bin-hadoop2.6/python/lib/py4j-0.8.2.1-src.zip/py4j/java_gateway.py", line 772, in __getattr__
  raise Py4JError('{0} does not exist in the JVM'.format(name))
       Py4JError: SparkConf does not exist in the JVM
  </code></pre>
  
  <p>Any idea what is the problem? Thank you for your help!</p>