jQuery Grid Plugin - jqGrid

I attempt to use jqGrid form editing with server confirmation.

There is a button with onclick

function() {

           var gr = $("#clientGrid").jqGrid("getGridParam","selrow");
           if( gr != null ) {

                           $("#clientGrid").jqGrid("editGridRow",  gr, {height:280, width:500, modal:true, reloadAfterSubmit:false},
                                                            {afterSubmit: function(response, postdata) {
                   var idvalue;

                   // some code
                    return [true, "oK", idvalue]
                }
            } );

}

but any response from the server bring the message: parsererror Status: 'parsererror'. Error code: 200 

Where is the trouble? What response I must send?

jQuery 1.6.1, jQuery-ui 1.8.13, jqGrid 4.1.1 are used.