jQuery Grid Plugin - jqGrid

this code works:

$grid->setPrimaryKeyId('SerialID');

$grid->setColProperty('SerialID', array(
    "width"=>"120",
    "label"=>"Ser. broj",
    "edittype"=>"select",
    "editrules"=>array("required"=>true),
    "editoptions"=>array("value"=>" :Select")
));

$grid->addCol(array(
    "editable"=>true,
    "hidden"=>true,
    "name"=>"Partner",
    "width"=>"100",
    "align"=>"center",
    "editoptions"=>array("defaultValue"=>$partner_name)
));

$serial_id = jqGridUtils::GetParam('SerialID');
$partner_id = jqGridUtils::GetParam('Partner');
$grid->setAfterCrudAction('add', "UPDATE serials SET Location = ? WHERE Serial=?",array($partner_id, $serial_id));
$grid->setAfterCrudAction('del', "UPDATE serials SET Location = 'skladiste' WHERE Serial=?",array($serial_id));

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this code doesn't work

$grid->setPrimaryKeyId('SerialID');

$grid->setColProperty('SerialID', array(
    "width"=>"120",
    "label"=>"Ser. broj",
    "edittype"=>"select",
    "editrules"=>array("required"=>true),
    "editoptions"=>array("value"=>" :Select")
));

$grid->addCol(array(
    "editable"=>true,
    "hidden"=>true,
    "name"=>"Partner",
    "width"=>"100",
    "align"=>"center",
    "editoptions"=>array("defaultValue"=>$partner_name)
));

$serial_id = jqGridUtils::GetParam('SerialID');
$partner_id = jqGridUtils::GetParam('Partner');
$grid->setAfterCrudAction('del', "UPDATE serials SET Location = ? WHERE Serial=?",array($partner_id, $serial_id));
$grid->setAfterCrudAction('add', "UPDATE serials SET Location = 'skladiste' WHERE Serial=?",array($serial_id));

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what am i doing wrong here?