title: Guid and DropDownList error?
body: <p>I am  trying to  fix yellow page of death on my asp.net application I dropDownList ddl_userNames with user Name  and Guid values  list I bind it using SQl data sours but my problem is I have item list value -1 and Select user and I have chart asp.net bind to this ddl_username   when I load the page it give me "Guid should contain 32 digits with 4 dashes (xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx)." I know it is because of -1 value can some one help to how to fix this problem  </p>
  
  <pre><code>&lt;asp:Content ID="Content1" ContentPlaceHolderID="HeadContent" runat="server"&gt;
      &lt;style type="text/css"&gt;
          .style1
          {
              height: 24px;
          }
      &lt;/style&gt;
  &lt;/asp:Content&gt;
  &lt;asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server"&gt;
      &lt;table class="ui-accordion"&gt;
          &lt;tr&gt;
              &lt;td&gt;
                  &lt;label&gt;Tech User name:&lt;/label&gt;&lt;/td&gt;
              &lt;td&gt;
                  &lt;asp:DropDownList ID="ddl_userNames" runat="server" 
                      DataSourceID="SqlDS_techNames" DataTextField="UserName" 
                      DataValueField="UserId" AppendDataBoundItems="True" AutoPostBack="True"&gt;
                      &lt;asp:ListItem Value="-1"&gt;Select one&lt;/asp:ListItem&gt;
                  &lt;/asp:DropDownList&gt;
                  &lt;asp:SqlDataSource ID="SqlDS_techNames" runat="server" 
                      ConnectionString="&lt;%$ ConnectionStrings:Compudata_ProjectManagerConnection %&gt;" 
                      SelectCommand="SELECT [UserId], [UserName] FROM [vw_aspnet_Users]"&gt;
                  &lt;/asp:SqlDataSource&gt;
              &lt;/td&gt;
          &lt;/tr&gt;
          &lt;tr&gt;
              &lt;td&gt;
                 &lt;label&gt;Sesrch terms:&lt;/label&gt; &lt;/td&gt;
              &lt;td&gt;
                                 &lt;asp:DropDownList ID="ddl_SesrchTerms" runat="server" 
                  &gt;
                                     &lt;asp:ListItem Value="-1"&gt;Select One&lt;/asp:ListItem&gt;
                                     &lt;asp:ListItem Value="1"&gt;Daily&lt;/asp:ListItem&gt;
                                     &lt;asp:ListItem Value="2"&gt;Weekly&lt;/asp:ListItem&gt;
                                     &lt;asp:ListItem Value="3"&gt;Monthly&lt;/asp:ListItem&gt;
                                 &lt;/asp:DropDownList&gt;&lt;/td&gt;
          &lt;/tr&gt;
          &lt;tr&gt;
              &lt;td&gt;
                  &lt;label&gt;Date:&lt;/label&gt;&lt;/td&gt;
              &lt;td&gt;
                  &lt;asp:TextBox ID="txtb_date" runat="server"&gt;&lt;/asp:TextBox&gt;
              &lt;/td&gt;
          &lt;/tr&gt;
          &lt;tr&gt;
              &lt;td class="style1"&gt;
                  &lt;asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Button" /&gt;
              &lt;/td&gt;
              &lt;td class="style1"&gt;
                  &lt;asp:Label ID="lbl_msg" runat="server"&gt;&lt;/asp:Label&gt;
              &lt;/td&gt;
          &lt;/tr&gt;
      &lt;/table&gt;
      &lt;br /&gt;
      &lt;br /&gt;
      &lt;br /&gt;
  
  
      &lt;asp:Chart ID="Chart1" runat="server" 
          DataSourceID="SqlDS_Get_Individual_Tech_Service_Chart"&gt;
          &lt;Series&gt;
              &lt;asp:Series Name="Series1" ChartType="Pie" XValueMember="billableTypeName" 
                  YValueMembers="TotalTime"&gt;
              &lt;/asp:Series&gt;
          &lt;/Series&gt;
          &lt;ChartAreas&gt;
              &lt;asp:ChartArea Name="ChartArea1"&gt;
              &lt;/asp:ChartArea&gt;
          &lt;/ChartAreas&gt;
      &lt;/asp:Chart&gt;
      &lt;asp:SqlDataSource ID="SqlDS_Get_Individual_Tech_Service_Chart" runat="server" 
          ConnectionString="&lt;%$ ConnectionStrings:Compudata_ProjectManagerConnection %&gt;" 
          SelectCommand="Get_Individual_Tech_Service_Chart" 
          SelectCommandType="StoredProcedure"&gt;
          &lt;SelectParameters&gt;
              &lt;asp:ControlParameter ControlID="ddl_SesrchTerms" DbType="Int32" 
                  Name="SearchTerms" PropertyName="SelectedValue" /&gt;
              &lt;asp:ControlParameter ControlID="ddl_techNames" DbType="Guid" Name="TechID" 
                  PropertyName="SelectedValue" /&gt;
              &lt;asp:ControlParameter ControlID="txtb_date" DbType="DateTime" Name="Date" 
                  PropertyName="Text" /&gt;
          &lt;/SelectParameters&gt;
      &lt;/asp:SqlDataSource&gt;
  &lt;/asp:Content&gt;
  </code></pre>