title: Why I'm getting 'Cannot redeclare drupal_error_levels()' error?
body: <p>I have one site running Drupal 7 on server and I get the following errors for the specific page and on specific action like (clearing cache, or page like '/calendar') otherwise site is running fine.</p>
  
  <blockquote>
    <p>Fatal error: Cannot redeclare drupal_error_levels() in includes/errors.inc on line 16 <br/>
    Fatal error: Cannot redeclare class QueryConditionInterface in includes/database/query.inc on line 16</p>
  </blockquote>
  
  <p>I am getting this errors on production server. If I run same code and database on my local server or any other server of Host provider it runs fine without errors.</p>
  
  <p>I don't know what causing this errors I have checked files also and there are no duplicate files.</p>