I downloaded the actual version from here.

Regards Andi

Here's the js code of it:

// JQuery
$(document).ready(function()
{
	// Globale Variablen
  var nSelectedLast,
      getColumnIndexByName = function(grid,columnName)
      {
          var cm = grid.jqGrid('getGridParam','colModel');
          for(var i=0; i<cm.length; i++)
          {
            if(cm[i].name===columnName)
            {
              return i;
            }
          }
          return -1;
      };

	// Funktionen
  function fnPickdates(nId)
  {
    $("#"+nId+"_Konfiguration_Datum","#Konfigurationen_Table").datepicker({dateFormat:"dd.mm.yy"}); 
  }


	// Grid
	$("#Konfigurationen_Table").jqGrid
	({
		// Options
		url:     "../includes/IncKonfigurationKonfigurationen.php?action=load",
		editurl: "../includes/IncKonfigurationKonfigurationen.php?action=save", 
    mtype: "POST",
		datatype: "json",
		caption: "Configurations",
		colNames:
		[
			'',
			'Date',
			'Time',
			'Datalogger SN',
			'Metering',
			'Technician'
		],
		colModel:
		[
			{name:'Action', width:'60px', fixed:true, sortable:false, resize:false, formatter:'actions', formatoptions:{keys:true}},
			{name:'Konfiguration_Datum', index:'Konfiguration_Datum', editable:true, edittype:'text', sorttype:"date", editoptions:{size: 10, maxlengh: 10, dataInit: function(element){$(element).datepicker({dateFormat: 'dd.mm.yy'})}}},
			{name:'Konfiguration_Zeit', index:'Konfiguration_Zeit', editable:true, sorttype:"time"},
			{name:'Konfiguration_Datalogger', index:'Konfiguration_Datalogger', editable:true, edittype:'text'},
			{name:'Konfiguration_Messintervall', width:'120px', index:'Konfiguration_Messintervall', editable:true, edittype:"select", formatter:'select', editoptions:{value:"0:Permanent;1:1 Hour;3:3 Hours;6:6 Hours;12:12 Hours;24:24 Hours"}},
			{name:'Konfiguration_Bearbeiter', index:'Konfiguration_Bearbeiter', editable:false, edittype:'text'}
		],
		sortname: 'Konfiguration_Datum desc, Konfiguration_Zeit',
		sortorder: "desc",
		rowNum: 10,
		pager: "#Konfigurationen_Pager",
		viewrecords: true,
		autowidth: true,
    shrinkToFit: false,
		height: "auto",

		// Events
		ondblClickRow: function(nId)
		{
			if(nId && nId!=nSelectedLast)
			{
				$(this).jqGrid('restoreRow',nSelectedLast);
				nSelectedLast=nId;
			}
			
      // Datensatz ändern
      $(this).jqGrid('editRow', nId, true, fnPickdates); 
		},

		subGrid: true,
		subGridRowExpanded: function(subgrid_id, row_id)
		{
			var subgrid_table_id, pager_id;
			subgrid_table_id = subgrid_id+"_t";
      pager_id = "p_"+subgrid_table_id;
			
			$("#"+subgrid_id).html("<table id='"+subgrid_table_id+"' class='scroll'></table><div id='"+pager_id+"' class='scroll'></div>");
      $("#"+subgrid_table_id).jqGrid
      ({
				// Options
        url:     "../includes/IncKonfigurationKonfigurationenSensoren.php?action=load&id="+row_id,
        editurl: "../includes/IncKonfigurationKonfigurationenSensoren.php?action=save&row_id="+row_id, 
        mtype: 'POST',
        datatype: "json",
        caption: "Sensors",
        colNames:
        [
          '',
          'Box',
          'Box Type',
          'Channel',
          'Sensor',
          'Metering',
          'Placement',
          'Relay',
          'Min',
          'Max',
          'Action',
          'Comment'
        ],
        colModel:
        [
          {name:'Action', width:'60px', fixed:true, sortable:false, resize:false, formatter:'actions', formatoptions:{keys:true}},
          {name:'Konfiguration_Sensor_Box', width:'60px', index:'Konfiguration_Sensor_Box', editable:true, edittype:"select", editoptions:{value:"1:1;2:2;3:3;4:4;5:5;6:6;7:7;8:8;9:9;10:10;11:11;12:12;13:13;14:14;15:15;16:16;17:17;18:18;19:19;20:20;99:99"}, align:'center'},
          {name:'Konfiguration_Sensor_Box_Typ', width:'80px', index:'Konfiguration_Sensor_Box_Typ', editable:true, edittype:"select", editoptions:{value:"Amp:Amplifier;Dis:Distributor"}},
          {name:'Konfiguration_Sensor_Box_Kanal', width:'60px', index:'Konfiguration_Sensor_Box_Kanal', editable:true, edittype:"select", editoptions:{value:"1:1;2:2;3:3;4:4"}, align:'center'},
          {name:'Sensor_Typ', index:'Sensor_Typ', editable:true, edittype:"select", formatter:'select', editoptions:{value:"3:CO?;2:Humi?;4:Radon?;1:Temp?;5:Virtual"}},
          {name:'Sensor_Messgroesse', index:'Sensor_Messgroesse', editable:false, edittype:"select", editoptions:{value:"1:Temperature [°C];2:Humidity rel [%rel];3:Humidity abs [g/m³];4:CO2 [ppm];5:Impulse [n];6:Frequency [Hz]"}},
          {name:'Konfiguration_Sensor_Platzierung', index:'Konfiguration_Sensor_Platzierung', editable:true, edittype:'text'},
          {name:'Konfiguration_Sensor_Relais', width:'60px', index:'Konfiguration_Sensor_Relais', editable:true, edittype:"select", editoptions:{value:":;1:1;2:2;3:3;4:4;5:5;6:6"}, align:'center'},
          {name:'Konfiguration_Sensor_Relais_Minimum', width:'50px', index:'Konfiguration_Sensor_Relais_Minimum', editable:true, edittype:'text', align:'center'},
          {name:'Konfiguration_Sensor_Relais_Maximum', width:'50px', index:'Konfiguration_Sensor_Relais_Maximum', editable:true, edittype:'text', align:'center'},
          {name:'Konfiguration_Sensor_Relais_Aktion', index:'Konfiguration_Sensor_Relais_Aktion', editable:true, edittype:"select", editoptions:{value:":;System On:System On;System Off:System Off;Exhauster On:Exhauster On;Exhauster Off:Exhauster Off"}},
          {name:'Konfiguration_Sensor_Bemerkung', index:'Konfiguration_Sensor_Bemerkung', editable:true, edittype:'text'}
        ],
        sortname: 'Konfiguration_Sensor_Box asc, Konfiguration_Sensor_Box_Kanal',
        sortorder: "asc",
        rowNum:10,
        pager: '#Konfigurationen_Pager'+subgrid_table_id,
        viewrecords: true,
//      autowidth: true,
        width:"100%",
        shrinkToFit: false,
        height: "auto",

        // Events
        ondblClickRow: function(nId)
        {
          if(nId && nId!=nSelectedLast)
          {
            $(this).jqGrid('restoreRow',nSelectedLast);
            nSelectedLast=nId;
          }
          
          // Datensatz ändern
          $(this).jqGrid('editRow', nId, true, fnPickdates); 
        },
      })

      // Grid Navigator
      $("#"+subgrid_table_id).jqGrid
      (
        'navGrid',
        "#"+pager_id,
        {add:true, edit:false, del:false, search:false},
        {
          // Edit
        },
        {
          // Add
          recreateForm: true,
          closeAfterAdd: true
        },
        {
          // Delete
        },
        {},
        {}
      );
		},
	});

	// Grid Navigator
	$("#Konfigurationen_Table").jqGrid
  (
  	'navGrid',
    "#Konfigurationen_Pager",
    {add:true, edit:false, del:false, search:false},
    {
    	// Edit
    },
    {
    	// Add
	    recreateForm: true,
      closeAfterAdd: true
    },
    {
    	// Delete
    },
    {},
    {}
  );



});

Our example page work fin with subgrids in IE9.

So little info is not enought to give you a help.

Regards

in IE9 JQGrid shows me a undefined line with every subgrid row, in FF everything is okay:

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