title: Magento enable cache creates page error Warning: simplexml_load_string()
body: <p>When i enable cache in the admin of our Magento (a new extensions requires us to do this), the store goes down and gives the following error on page load.</p>
  
  <pre><code>    Warning: simplexml_load_string() [function.simplexml-load-string]: Entity: line 51: parser error : StartTag: invalid element name  in /home/sitename/public_html/lib/Varien/Simplexml/Config.php on line 383
  
  #0 [internal function]: mageCoreErrorHandler(2, 'simplexml_load_...', '/home/sitename...', 383,   Array)
  #1 /home/sitename/public_html/lib/Varien/Simplexml/Config.php(383): simplexml_load_string('loadCache()
  #3 /home/sitename/public_html/app/code/core/Mage/Core/Model/App.php(408): Mage_Core_Model_Config-&gt;loadModulesCache()
  #4 /home/sitename/public_html/app/code/core/Mage/Core/Model/App.php(338): Mage_Core_Model_App-&gt;_initModules()
  #5 /home/sitename/public_html/app/Mage.php(640): Mage_Core_Model_App-&gt;run(Array)
  #6 /home/sitename/public_html/index.php(80): Mage::run('', 'store')
  #7 {main}
  </code></pre>
  
  <p>We cannot load the store anymore.</p>