Cannot redeclare class /fckeditor.php line 29

Search in all files for lines that include fckeditor.php file:

include "fckeditor.php";
require "fckeditor.php";

and replace them with "xxx_once" calls :

include_once "fckeditor.php";
require_once "fckeditor.php";

Note that those include/require lines may look a bit differently, e.g.:

include(DIR_WS_INCLUDES. 'FCKeditor/fckeditor.php');