Rowtoquery is null or not an object Error

Thanks for replying back. I tried your suggestion but now I get "Element is null or not an object" error for each row. my ASPx code is here:

<igtbl:UltraWebGrid ID="UltraWebGrid1" runat="server" Browser="Xml"

DataSourceID="dsMddDataMap" Height="200px"

Width="700px" oninitializerow="UltraWebGrid1_InitializeRow">

<Bands>

<igtbl:UltraGridBand AddButtonCaption="LookupMDD" BaseTableName="LookupMDD"

Key="LookupMDD">

<igtbl:UltraGridColumn BaseColumnName="LookupRDBID" DataType="System.Int32"

IsBound="True" Key="LookupRDBID" Hidden="True">

</Header>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="Surveycode" DataType="System.Int32"

IsBound="True" Key="Surveycode" Hidden="True">

</Header>

</Footer>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="ElementName" IsBound="True"

Key="ElementName">

</Header>

</Footer>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="VariableName" IsBound="True"

Key="VariableName">

</Header>

</Footer>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="VariableID" DataType="System.Int32"

IsBound="True" Key="VariableID">

</Header>

</Footer>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="Response" DataType="System.Int32"

IsBound="True" Key="Response">

</Header>

</Footer>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="PTKVariable" IsBound="True"

Key="PTKVariable" Hidden="True">

</Header>

</Footer>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="CCP" IsBound="True" Key="CCP"

Hidden="True">

</Header>

</Footer>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="FixValue" IsBound="True" Key="FixValue"

Hidden="True">

</Header>

</Footer>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="DateAdded" DataType="System.DateTime"

IsBound="True" Key="DateAdded">

</Header>

</Footer>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="DateModified" DataType="System.DateTime"

IsBound="True" Key="DateModified">

</Header>

</Footer>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="DateDeleted" DataType="System.DateTime"

IsBound="True" Key="DateDeleted">

</Header>

</Footer>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="IsValid" DataType="System.Boolean"

IsBound="True" Key="IsValid" Type="CheckBox">

</Header>

</Footer>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="Verified" DataType="System.Boolean"

IsBound="True" Key="Verified" Type="CheckBox">

</Header>

</Footer>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="IsLock" DataType="System.Boolean"

IsBound="True" Key="IsLock" Type="CheckBox">

</Header>

</Footer>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="MDDFileName" IsBound="True"

Key="MDDFileName" Hidden="True">

</Header>

</Footer>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="VariableText" IsBound="True"

Key="VariableText">

</Header>

</Footer>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="MapTable" IsBound="True" Key="MapTable"

Type="DropDownList">

</Header>

</Footer>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="MapField" IsBound="True" Key="MapField"

Type="DropDownList">

</Header>

</Footer>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="MapLen" DataType="System.Int32"

IsBound="True" Key="MapLen">

</Header>

</Footer>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="WMDvalue" IsBound="True" Key="WMDvalue">

</Header>

</Footer>

</igtbl:UltraGridColumn>

</Columns>

</AddNewRow>

</igtbl:UltraGridBand>

</Bands>

<DisplayLayout AllowUpdateDefault="Yes" BorderCollapseDefault="Separate"

FixedHeaderIndicatorDefault="Button" LoadOnDemand="Xml" Name="UltraWebGrid1"

RowHeightDefault="20px" TableLayout="Fixed" UseFixedHeaders="True"

Version="4.00" AllowColSizingDefault="Free" SelectTypeCellDefault="Single"

SelectTypeRowDefault="Single" ViewType="OutlookGroupBy">

</FrameStyle>

</ActivationObject>

</DisplayLayout>

</igtbl:UltraWebGrid>

<igcmbo:WebCombo ID="cmboTables" runat="server" DataSourceID="dsTableName"

EnableXmlHTTP="True" SelBackColor="" SelForeColor="" Version="4.00"

DataTextField="tblname" DataValueField="tblname"

onselectedrowchanged="cmboTables_SelectedRowChanged">

<igtbl:UltraGridColumn IsBound="True" BaseColumnName="tblname" Key="tblname">

</Header>

</igtbl:UltraGridColumn>

</Columns>

<DropDownLayout Version="4.00" BaseTableName="tmpTable"

XmlLoadOnDemandType="Accumulative" DropdownWidth="135px">

</DropDownLayout>

</igcmbo:WebCombo>

<igcmbo:WebCombo ID="cmboColumnname" runat="server" DataSourceID="dsColumnName"

EnableXmlHTTP="True" SelBackColor="" SelForeColor="" Version="4.00" DropDownLayout-DropdownWidth="170px" DropDownLayout-ColWidthDefault="150px">

<igtbl:UltraGridColumn BaseColumnName="Databound Col0" IsBound="True"

Key="Databound Col0">

</Header>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="Databound Col1" DataType="System.Int32"

IsBound="True" Key="Databound Col1">

</Header>

</Footer>

</igtbl:UltraGridColumn>

<igtbl:UltraGridColumn BaseColumnName="Databound Col2" IsBound="True"

Key="Databound Col2">

</Header>

</Footer>

</igtbl:UltraGridColumn>

</Columns>

<DropDownLayout BaseTableName="" Version="4.00"

XmlLoadOnDemandType="Accumulative" DropdownWidth="195px">

</FrameStyle>

</DropDownLayout>

</igcmbo:WebCombo>

and my code behind is:

protected void UltraWebGrid1_InitializeRow(object sender, RowEventArgs e)

{

if (!IsPostBack)

{

//make sure the grid allows for editing

//this.UltraWebGrid1.DisplayLayout.AllowUpdateDefault = Infragistics.WebUI.UltraWebGrid.AllowUpdate.Yes;

//assign the webcombo as an editor for the CategoryID column in the grid

this.UltraWebGrid1.DisplayLayout.Bands[0].Columns.FromKey("MapTable").Type = Infragistics.WebUI.UltraWebGrid.ColumnType.DropDownList;

this.UltraWebGrid1.DisplayLayout.Bands[0].Columns.FromKey("MapTable").EditorControlID = this.cmboTables.UniqueID;

this.UltraWebGrid1.DisplayLayout.Bands[0].Columns.FromKey("MapField").Type = Infragistics.WebUI.UltraWebGrid.ColumnType.DropDownList;this.UltraWebGrid1.DisplayLayout.Bands[0].Columns.FromKey("MapField").EditorControlID = this.cmboColumnname.UniqueID;

}

protected void cmboTables_SelectedRowChanged(object sender, Infragistics.WebUI.WebCombo.SelectedRowChangedEventArgs e)

{

this.dsColumnName.SelectParameters[0].DefaultValue = this.cmboTables.DisplayValue.ToString();

}

protected void dsColumnName_Selecting(object sender, ObjectDataSourceSelectingEventArgs e)

{

try

{

e.InputParameters[0] = this.cmboTables.SelectedRow.Cells[0].Value.ToString();

}

catch

{

}

Thanks.