So, I figured this out. Looking around I found post #452, which shows actual code for the init_yclass.php file. I took the functions from the yclass and put them at the bottom of my /admin/includes/classes/xsell_advanced.php file, like so:

PHP Code:
/***** START ADDING Y-CLASS METHODS NEVER INCLUDED IN INSTALLATION *****/
    
function db_result_to_string($glue$db_result){
        
$temp_array = array();
        if(
$this->is_obj($db_result,'queryFactoryResult')){
            
// We need to clone, because we don't want to touch the real object
            
while(!$db_result->EOF){
                
$temp_array[] = $db_result->fields['products_'.XSELL_FORM_INPUT_TYPE];
                
$db_result->MoveNext();
            }
            
$db_result->Move(0);
            
$db_result->MoveNext();
        }
        
        return 
implode($glue,$temp_array);
    }
    
    
// This function does not work for all languages! BEWARE
    
function array_to_upper(&$entries){
        foreach(
$entries as $entry){
            
$entry strtoupper($entry);
        }
    }
    
    
// http://us3.php.net/manual/en/function.is-object.php#66370
    
function is_obj( &$object$check=null$strict=true ){
        if (
is_object($object)) {
            if (
$check == null) {
                return 
true;
              } else {
                
$object_name get_class($object);
                return (
$strict === true)?( $object_name == $check ):( strtolower($object_name) == strtolower($check) );
              }   
          } else {
            return 
false;
          }
    }
    
/***** END ADDING Y-CLASS METHODS NEVER INCLUDED IN INSTALLATION *****/ 
Everything seems to work fine now in the admin area.
Hope this helps.

Quote Originally Posted by xzistance View Post
Hey Sheryll,

Have you found a solution for this by chance? I'm getting the same issue. I can add products to cross-sell, but editing/deleting/searching all break on this error. Basically the admin aspect of this is breaking. I'm looked in to the error more and that function just doesn't exist.. pretty ridiculous, but I'm trying to figure out what exactly it was doing and seeing if I can replicate what it should be doing.