Sorting i Gridview virker ikke

Hej
Jeg kan ikke sortere mine to kolonner i flg. GridView:

<asp:GridView ID="GridVendors" runat="server" AllowSorting="True" BorderWidth="1px" AutoGenerateColumns="false" Width="505px">
<HeaderStyle CssClass="DataGridHeader" />
<Columns>
    <asp:BoundField DataField="VendorName" SortExpression="VendorName" HeaderText="Leverand&#248;r" />
        <asp:BoundField DataField="AccountID" SortExpression="VendorUserFullName" HeaderText="Konto" />
</Columns>
</asp:GridView>

Jeg får bl.a. fejlmedd.:
[HttpException (0x80004005): GridView 'GridVendors' udløste handlingen Sorting, der ikke blev håndteret.]
  System.Web.UI.WebControls.GridView.OnSorting(GridViewSortEventArgs e) +1471691
  System.Web.UI.WebControls.GridView.HandleSort(String sortExpression, SortDirection sortDirection) +76
  System.Web.UI.WebControls.GridView.HandleSort(String sortExpression) +70
  System.Web.UI.WebControls.GridView.HandleEvent(EventArgs e, Boolean causesValidation, String validationGroup) +552
  System.Web.UI.WebControls.GridView.RaisePostBackEvent(String eventArgument) +199
  System.Web.UI.WebControls.GridView.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +7
  System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +11
  System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +174
  System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +5102


Er her nogen som kan gennemskue hvad, der er galt?

/henrik