Thanks for reporting this issue (unable to export hidden columns), it would be fixed in next version.
Meanwhile you can apply this workaround.
var CM = $("#grid_export").pqGrid('getColModel');
for(var i=0;i< CM.length; i++){
var column = CM[i];
if(column.hidden){
column._width = parseInt( column.width);
}
}
$("#grid_export").pqGrid("exportExcel", { url: "/pro/demos/excel", sheetName: "pqGrid sheet" });