After spending a lot of time trying to recreate the error on a small project so later I could send it to you, as requested, I was able to find the cause.

Setting the property Browser="Xml" will throw the exception mentioned before.

I found out about this by applying the following Skin:

<igtbl:UltraWebGrid runat="server" 
  Browser="Xml"
  ImageDirectory="~/App_Themes/Default/Office2007Blue/WebGrid/">                       
  <DisplayLayout
    AllowColSizingDefault="Free"
    AllowColumnMovingDefault="OnServer"
    AllowDeleteDefault="Yes"
    AllowUpdateDefault="Yes"
    AllowSortingDefault="Yes"
    BorderCollapseDefault="Separate"
    CellClickActionDefault="RowSelect"
    CompactRendering="True"
    GridLinesDefault="NotSet"
    LoadOnDemand="Automatic"
    Name="ctl12xUltraWebGrid1"
    RowHeightDefault="20px"
    RowSelectorsDefault="No"
    SelectTypeRowDefault="Extended"
    StationaryMargins="Header"
    StationaryMarginsOutlookGroupBy="True"
    TableLayout="Fixed"
    Version="4.00"
    ViewType="OutlookGroupBy"    
    HeaderClickActionDefault="SortMulti"
    NoDataMessage ="No records were found">
    <GroupByBox>
      <BandLabelStyle
        CssClass="igwgGrpBoxBandLblBlue2k7">
      </BandLabelStyle>
      <Style
        CssClass="igwgGrpBoxBlue2k7">
      </Style>
    </GroupByBox>
    <GroupByRowStyleDefault CssClass="igwgGrpRowBlue2k7"></GroupByRowStyleDefault>
    <ActivationObject BorderColor="181, 196, 223" BorderWidth="">
      <BorderDetails WidthLeft="0px" WidthRight="0px" />
    </ActivationObject>
    <RowExpAreaStyleDefault CssClass="igwgRowExpBlue2k7"></RowExpAreaStyleDefault>
    <FooterStyleDefault CssClass="igwgFooterBlue2k7"></FooterStyleDefault>
    <SelectedGroupByRowStyleDefault CssClass="igwgGrpRowSelBlue2k7"></SelectedGroupByRowStyleDefault>
    <RowStyleDefault CssClass="igwgRowBlue2k7" Cursor="Hand">           
      <BorderDetails WidthBottom="1px" WidthTop="1px" />
      <Padding Left="3px" />
    </RowStyleDefault>   
    <FilterOptionsDefault AllowRowFiltering="OnServer" FilterUIType="FilterRow" FilterComparisonType="CaseInsensitive" RowFilterMode="AllRowsInBand" >
      <FilterOperandDropDownStyle BackColor="White" BorderColor="Silver" BorderStyle="Solid"
        BorderWidth="1px" CustomRules="overflow:auto;" Font-Names="Verdana,Arial,Helvetica,sans-serif"
        Font-Size="11px">
        <Padding Left="2px" />
      </FilterOperandDropDownStyle>
      <FilterHighlightRowStyle BackColor="#151C55" ForeColor="White">
      </FilterHighlightRowStyle>
      <FilterDropDownStyle BackColor="White" BorderColor="Silver" BorderStyle="Solid" BorderWidth="1px"
        CustomRules="overflow:auto;" Font-Names="Verdana,Arial,Helvetica,sans-serif" Font-Size="11px"
        Width="200px">
        <Padding Left="2px" />
      </FilterDropDownStyle>
    </FilterOptionsDefault>
    <RowSelectorStyleDefault CssClass="igwgRowSlctrBlue2k7"></RowSelectorStyleDefault>           
    <FixedHeaderStyleDefault CssClass="igwgHdrFxdBlue2k7"></FixedHeaderStyleDefault>
    <SelectedRowStyleDefault CssClass="igwgRowSelBlue2k7"></SelectedRowStyleDefault>
    <HeaderStyleDefault CssClass="igwgHdrBlue2k7" Height="23px"></HeaderStyleDefault>
    <RowAlternateStyleDefault CssClass="igwgRowAltBlue2k7"></RowAlternateStyleDefault>
    <Images
      ImageDirectory="~/App_Themes/Default/Office2007Blue/WebGrid/">
    </Images>
    <SelectedHeaderStyleDefault CssClass="igwgHdrSelBlue2k7"></SelectedHeaderStyleDefault>
    <FormulaErrorStyleDefault CssClass="igwgFormulaErrBlue2k7"></FormulaErrorStyleDefault>
    <EditCellStyleDefault CssClass="igwgCellEdtBlue2k7"></EditCellStyleDefault>
    <FrameStyle CssClass="igwgFrameBlue2k7" Width="100%" Height="300px"></FrameStyle>
    <FixedCellStyleDefault CssClass="igwgCellFxdBlue2k7"></FixedCellStyleDefault>
    <FixedFooterStyleDefault CssClass="igwgFtrFxdBlue2k7"></FixedFooterStyleDefault>
    <Pager AllowPaging="True" PageSize="100"  StyleMode="PrevNext" >
      <Style CssClass="igwgPgrBlue2k7"></Style>
    </Pager>
    <AddNewBox Hidden="False"  Prompt="Add" View="Compact" >
      <ButtonStyle CssClass="igwgAddNewBtnBlue2k7"></ButtonStyle>
      <Style CssClass="igwgAddNewBoxBlue2k7"></Style>
    </AddNewBox> 
  </DisplayLayout>
</igtbl:UltraWebGrid>

Let me know if you still need me to send you the project. 

THANKS ! 

void WebNavBar1_AfterMoveForward(object sender, Infragistics.WebUI.WebNavBar.AfterNavigateEventArgs args)
{
    UWGrdProjects.DataBind();
} 

Hope that helps.

Best,
Nick

 hey thanks !, now it seems to work better, I thought I did this before.... weird.

Anyway, there is still something.

 After adding your code and running the application If you change the page using the Forward or the Reverse button and then click the Next or the  Previous button, it won't change the active row, or at least it won't select it, even if I add:

  protected void WebNavBar1_ChangeActiveRow(object sender, Infragistics.WebUI.WebNavBar.AfterNavigateEventArgs args)
  {
    UWGrdProjects.DisplayLayout.ActiveRow.Selected = true;
  }

   OnAfterMoveNext="WebNavBar1_ChangeActiveRow"
                OnAfterMovePrev="WebNavBar1_ChangeActiveRow"

UPDATE: Clicking the Forward and the Reverse buttons will change the page. but for some reason when I click the Next or Previous buttons it will highlight the row in the previous page, I found out this by going back to the previous page after clicking the Next or Previous buttons.

any ideas?

thanks again for your help !! 

ureyes84 said:

changing the value of Browser from "Xml" to "Auto" will "fix" it. However, it makes the grid look weird the first time it loads

I noticed this keeps the app from crashing when clicking the WebNavBar, however, as stated above,  the grid will render differently when the page is refreshed.

This  is an email I got from Nick, which fixed my problem, so I hope this helps someone else.

 --------------------------------------

Hm, this seems to be a bug in the Grid, here is an easy workaround:

     <igtbl:UltraWebGrid ID="UWGrdProjects" runat="server" Width="100%" Height="140px" Browser="Auto">       

          <DisplayLayout LoadOnDemand="Xml" SelectTypeRowDefault="Single">

                <HeaderStyleDefault

                          CssClass=""

                          Font-Names="Verdana, Arial, Helvetica, sans-serif"

                          Font-Size="11px"

                          BackColor="#D4D7DB"

                          BackgroundImage="App_Themes/Default/Office2007Blue/WebGrid/igwgHeader.jpg">

                     <Padding Left="10px" Right="10px" />

                </HeaderStyleDefault>

                <Pager AllowPaging="true"  PageSize="5" ></Pager>

          </DisplayLayout>

     </igtbl:UltraWebGrid>

The idea is to put a HeaderStyleDefault section below DisplayLayout and set its CssClass to Empty, then set Font, BackGround, Padding etc. however you like.

  --------------------------------------

thanks Nick.

The page where my grid is contains multiple UpdatePanel controls. I noticed after removing them, the grid was keeping the active row selected. I'm still getting the exception when:

Browser="Xml"
   LoadOnDemand="Xml"

So any help would be appreciated. 

 Ok now I'm getting the exception again.

 Setting

   Browser="Xml"
   LoadOnDemand="Xml" 

 will make the app crash , even with the DataBind on the OnAfterMoveBackward

changing the value of Browser from "Xml" to "Auto" will "fix" it. However, it makes the grid look weird the first time it loads

So is this a bug? or is it just that these settings are incompatible with the navbar?

Thanks !