« MODx Parse Error »

MODx encountered the following error while attempting to parse the requested resource:
« PHP Parse Error »
PHP error debug
  Error: array_key_exists() [function.array-key-exists]: The second argument should be either an array or an object 
  Error type/ Nr.: Warning - 2 
  File: /home/johnan9/public_html/manager/includes/document.parser.class.inc.php 
  Line: 923 
  Line 923 source: if (!is_numeric($identifier) && array_key_exists($identifier, $this->documentListing)) {  
Parser timing
  MySQL: 0.0122 s(2 Requests)
  PHP: 0.1331 s 
  Total: 0.1454 s