I just moved from PHP 5.2 to 5.4 and I now get this message, even before trying to display a grid:
Declaration of GridConnector::fill_collections() should be compatible with Connector::fill_collections()
The message is issued as soon as I require the DHTMLX connector file:
require_once(dirname(FILE)."/…/…/dhtmlx/connector/grid_connector.php");
If I go back to PHP 5.2 everything is OK again.