error when trying to use guid to mark groups of files as belonging together when uploaded together

I am using asp.net, (VB but C# code ok for answer if you prefer), to write a web page that allows a user to upload multiple files and mark them so that they c an be grouped together/filtered for downloading.

The code behind for this page is:

Imports System.IO
Imports System.Data
Imports System.Data.SqlClient
Imports System.Configuration
Partial Class BulkUploadPRIVATEPhysicianFiles
  Inherits System.Web.UI.Page

  Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
    If Not IsPostBack Then
      BindGrid()
    End If
    '  Page.Header.Title = "Bulk Upload Private Physician Files Page"

  End Sub

  Private Sub BindGrid()
    Dim QuantumConnectionString3 As String = ConfigurationManager.ConnectionStrings("QuantumConnectionString3").ConnectionString
    Using con As New SqlConnection(QuantumConnectionString3)
      Using cmd As New SqlCommand()
        cmd.CommandText = "select Id, Name, IsItPrivate, Related, WhenUploaded from tblFiles where IsItPrivate = 1 order by related,WhenUploaded, name"
        cmd.Connection = con
        con.Open()
        GridView1.DataSource = cmd.ExecuteReader()
        'GridView1.Sort("Related", SortDirection.Ascending)
        GridView1.DataBind()
        con.Close()
      End Using
    End Using
  End Sub


  Protected Sub Upload(sender As Object, e As EventArgs)

    If FileUpload1.HasFiles Then
      If FileUpload1.PostedFiles.Count = 1 Then
        SaveFile(FileUpload1.PostedFiles.FirstOrDefault())
      Else
        Dim related As Guid = Guid.NewGuid
        For Each file In FileUpload1.PostedFiles
          SaveFile(file, related)
        Next
      End If
    End If

  End Sub

  Private Sub SaveFile(ByRef AFile As HttpPostedFile, Optional ByVal AGuid As Guid = Guid.Empty)

    Const QUERY As String = "INSERT INTO tblFiles VALUES ( @Name, @ContentType, @IsItPrivate, @Data,@Related );"

    Dim filename As String = Path.GetFileName(AFile.FileName)
    Dim contentType As String = AFile.ContentType

    Using fileStream As Stream = AFile.InputStream
      Using br As New BinaryReader(fileStream)
        Dim bytes As Byte() = br.ReadBytes(DirectCast(fileStream.Length, Long))
        Using connection As New SqlConnection(ConfigurationManager.ConnectionStrings("constr").ConnectionString)
          Using command As New SqlCommand(QUERY, connection)
            command.Parameters.Add("@Name", SqlDbType.VarChar).Value = filename
            command.Parameters.Add("@ContentType", SqlDbType.VarChar).Value = contentType
            command.Parameters.Add("@Data", SqlDbType.Binary).Value = bytes
            command.Parameters.Add("@IsItPrivate", SqlDbType.Bit).Value = 1
            If AGuid <> Guid.Empty Then
              command.Parameters.Add("@Related", SqlDbType.VarChar).Value = AGuid
            Else
              command.Parameters.Add("@Related", SqlDbType.VarChar).Value = DBNull
              Response.Write("oh-oh")
            End If

            connection.Open()
            command.ExecuteNonQuery()
            connection.Close()
          End Using
        End Using
      End Using
    End Using

  End Sub




  Protected Sub UploadOrig(sender As Object, e As EventArgs)
    If FileUpload1.HasFiles Then
      For Each file In FileUpload1.PostedFiles
        Using fs As Stream = file.InputStream
          Dim filename As String = Path.GetFileName(file.FileName)
          Dim contentType As String = file.ContentType
          Using br As New BinaryReader(fs)
            Dim bytes As Byte() = br.ReadBytes(DirectCast(fs.Length, Long))
            'Dim WhenUploaded As DateTime = DateTime.ParseExact(System.DateTime.Now, "yyyy-MM-dd", Nothing)
            Dim WhenUploaded As DateTime = System.DateTime.Now
            Dim QuantumConnectionString3 As String = ConfigurationManager.ConnectionStrings("QuantumConnectionString3").ConnectionString
            Using con As New SqlConnection(QuantumConnectionString3)
              Dim query As String = "insert into tblFiles values (@Name, @ContentType,@IsItPrivate, @Data, @Related, @WhenUploaded)"
              Using cmd As New SqlCommand(query)
                cmd.Connection = con
                cmd.Parameters.Add("@Name", SqlDbType.VarChar).Value = filename
                cmd.Parameters.Add("@ContentType", SqlDbType.VarChar).Value = contentType
                cmd.Parameters.Add("@Data", SqlDbType.Binary).Value = bytes
                cmd.Parameters.Add("@IsItPrivate", SqlDbType.Bit).Value = 1
                'cmd.Parameters.Add("@Related", SqlDbType.VarChar).Value = TryCast(FindControl("DropDownList1"), DropDownList).SelectedIndex
                'cmd.Parameters.Add("@Related", SqlDbType.VarChar).Value = "ReportGroup2"
                cmd.Parameters.AddWithValue("@Related", DropDownList1.SelectedValue)
                cmd.Parameters.Add("@WhenUploaded", SqlDbType.DateTime).Value = WhenUploaded
                con.Open()
                cmd.ExecuteNonQuery()
                con.Close()
              End Using
            End Using
          End Using
        End Using
      Next
      Response.Redirect(Request.Url.AbsoluteUri)
    End If
  End Sub

  Protected Sub DownloadFile(sender As Object, e As EventArgs)
    Dim id As Integer = Integer.Parse(TryCast(sender, LinkButton).CommandArgument)
    Dim bytes As Byte()
    Dim fileName As String, contentType As String, Related As String
    Dim IsItPrivate As Boolean
    Dim WhenUploaded As DateTime
    Dim QuantumConnectionString3 As String = ConfigurationManager.ConnectionStrings("QuantumConnectionString3").ConnectionString
    Using con As New SqlConnection(QuantumConnectionString3)
      Using cmd As New SqlCommand()
        cmd.CommandText = "select Name, Data, ContentType, IsItPrivate, Related, WhenUploaded from tblFiles where Id=@Id and IsItPrivate=1 and Related = 1 order by Related, WhenUploaded,Name"
        cmd.Parameters.AddWithValue("@Id", id)
        cmd.Parameters.AddWithValue("@IsItPrivate", IsItPrivate)
        cmd.Parameters.AddWithValue("@Related", Related)
        cmd.Parameters.AddWithValue("@WhenUploaded", WhenUploaded)
        cmd.Connection = con
        con.Open()
        Using sdr As SqlDataReader = cmd.ExecuteReader()
          sdr.Read()
          bytes = DirectCast(sdr("Data"), Byte())
          contentType = sdr("ContentType").ToString()
          fileName = sdr("Name").ToString()
          IsItPrivate = sdr("IsItPrivate").ToString()
          Related = sdr("Related").ToString()
          ' WhenUploaded = sdr("WhenUploaded").ToString()
        End Using
        con.Close()
      End Using
    End Using
    Response.Clear()
    Response.Buffer = True
    Response.Charset = ""
    Response.Cache.SetCacheability(HttpCacheability.NoCache)
    Response.ContentType = contentType
    Response.AppendHeader("Content-Disposition", "attachment; filename=" + fileName)
    Response.BinaryWrite(bytes)
    Response.Flush()
    Response.End()
  End Sub


  Protected Sub Page_PreRender(sender As Object, e As EventArgs) Handles Me.PreRender
    Dim aa As Label = Page.Master.FindControl("a")
    aa.Text = "Upload/Download Private Reports"
  End Sub
End Class

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and the markup is:

<%@ Page Language="VB" AutoEventWireup="false" CodeFile="BulkUploadPRIVATEPhysicianFiles.aspx.vb" MaintainScrollPositionOnPostback="true"
  Inherits="BulkUploadPRIVATEPhysicianFiles" MasterPageFile="~/MasterPages/PhysicianTwoPartMasterPage.master" %>

<asp:Content ID="Content1" ContentPlaceHolderID="headw" runat="Server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="cpMainContent" runat="Server">

  <table>
    <tr>
      <td>
        <h6>UPLOAD FILES</h6>
      </td>
      <td>&nbsp;</td>
     
    </tr>
    <tr>
      <td>
        <asp:FileUpload ID="FileUpload1" runat="server" AllowMultiple="true" /></td>
       
        <td></td>
          </tr>
    <tr>
       <td> <asp:Button ID="btnUpload" runat="server" Text="Upload" OnClick="Upload" /></td>
      <td> <hr /></td>
      <td><hr style="border-style:ridge" /></td>
    </tr>
    <tr>
 

      <td>
     
        <asp:GridView ID="GridView1" runat="server" HeaderStyle-BackColor="#3AC0F2" HeaderStyle-ForeColor="White"
          RowStyle-BackColor="#A1DCF2" AlternatingRowStyle-BackColor="White" AlternatingRowStyle-ForeColor="#000"
          AutoGenerateColumns="false" AllowSorting="true">
          <Columns>
            <asp:BoundField DataField="Related" HeaderText="Report Group" />
            <asp:BoundField DataField="Name" HeaderText="File Name" />
            <asp:BoundField DataField="WhenUploaded" HeaderText="When Uploaded" />
            <asp:TemplateField ItemStyle-HorizontalAlign="Center">
              <ItemTemplate>
                <asp:LinkButton ID="lnkDownload" ForeColor="#ff6600" BorderColor="#0082c8" runat="server" Text="Download" OnClick="DownloadFile"
                  CommandArgument='<%# Eval("Id") %>'></asp:LinkButton>
              </ItemTemplate>
            </asp:TemplateField>
          </Columns>
        </asp:GridView>
      </td>
    </tr>
    <tr>
      <asp:DropDownList ID="DropDownList1" runat="server" DataSourceID="ReportGroupDataSource" 
        DataTextField="Related" DataValueField="Related" AutoPostBack="True"></asp:DropDownList>
      <td></td>
    </tr>
    <asp:SqlDataSource ID="ReportGroupDataSource" runat="server"
      SelectCommand="SELECT * FROM [ReportGroup] ORDER BY [Related]" 
      ConnectionString='<%$ ConnectionStrings:QuantumConnectionString3 %>'>
    </asp:SqlDataSource>
  </table>
  <div class="clear"></div>

  <div id="footer">
    <div id="footer-3">
      <span id="copyright">&copy; <%=DateTime.Now.Year %> - {tiny nonprofit}
        <br />
        <asp:LoginName ID="LoginName1" runat="server"
          FormatString="Logged in as: {0}" />
      </span>
    </div>
  </div>
</asp:Content>

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The error i'm seeing is:



My ultimate goal is to allow a user to upload a batch of files that will all be marked with the related field so that on that same page, the files will appear in the gridview ready for downloading. My next step is to have the downloadable files in a gridview on a webpage that the physician user sees so that he can tell which supporting files go with which report.  THe user who uploads the files (a clerical) will be instructed to upload all related files (report and supporting docs together).  The physician will see the gridview sorted such that the files that belong together will have the same guid.

Thank you if you're still with me, reading.  My management told me the doctors are helpless/too busy so it must be something that they can tell at a glance.  Hence my requirement that everything be "automatic".