Fatal error: Call to a member function on a non-object in ...

Fatal error: Call to a member function on a non-object in /home/[site path omitted]/classes/mambo.php on line 1614

I now get this message upon entry to my site - Can anyone tell me what this means and how to fix it? (I have omitted the site paths)
The line from the file it refers to is highlighted here in blue. I have posted an excerpt to assist:

/**
* Checks whether a menu option is within the users access level
* @param int Item id number
* @param string The menu option
* @param int The users group ID number
* @param database A database connector object
* @return boolean True if the visitor's group at least equal to the menu access
*/
function mosMenuCheck( $Itemid, $menu_option, $gid, &$db ) {
$dblink="index.php?option=$menu_option";
$db->setQuery( "SELECT access FROM #__menu WHERE id='$Itemid' OR link='$dblink'" );
$access = intval( $db->loadResult() );
return ($access <= $gid);
}

Any help would be appreciated...
Regards,
Chris.

[maalder]

**** wrong item ****