Index was out of range. Must be non-negative and less than the size of the collection. (GridView)

Index was out of range. Must be non-negative and less than the size of the collection.

    Protected Sub lnkDownload_Click(ByVal sender As Object, ByVal e As EventArgs)
        Dim lnkbtn As LinkButton = TryCast(sender, LinkButton)
        Dim gvrow As GridViewRow = TryCast(lnkbtn.NamingContainer, GridViewRow)

        Dim fileid As Integer = Convert.ToInt32(GridView1.DataKeys(gvrow.RowIndex).Value.ToString())
        
        Dim con As New SqlConnection("Data Source=BRIAN-PC\SQLEXPRESS;Initial Catalog=master_db;Integrated Security=True;")



        Using cmd As New SqlCommand()
            cmd.CommandText = "Select content_name, content_type, content_file from content where content_id=@Id"
            cmd.Parameters.AddWithValue("@Id", SqlDbType.Int).Value = 1
            cmd.Connection = con
            con.Open()

            Dim dt As DataTable = GetData(cmd)

            If dt IsNot Nothing Then

                download(dt)

            End If
           
        End Using

    End Sub


    Public Function GetData(ByVal cmd As SqlCommand) As DataTable

        Dim dt As New DataTable

        Dim strConnString As String = System.Configuration.ConfigurationManager.ConnectionStrings("ConnStringDb1").ConnectionString()

        Dim con As New SqlConnection(strConnString)

        Dim sda As New SqlDataAdapter

        cmd.CommandType = CommandType.Text

        cmd.Connection = con

        Try

            con.Open()

            sda.SelectCommand = cmd

            sda.Fill(dt)

            Return dt

        Catch ex As Exception

            Response.Write(ex.Message)

            Return Nothing

        Finally

            con.Close()

            sda.Dispose()

            con.Dispose()

        End Try

    End Function


    Protected Sub download(ByVal dt As DataTable)

        Dim bytes() As Byte = CType(dt.Rows(0)("Data"), Byte())

        Response.Buffer = True

        Response.Charset = ""

        Response.Cache.SetCacheability(HttpCacheability.NoCache)

        Response.ContentType = dt.Rows(0)("ContentType").ToString()

        Response.AddHeader("content-disposition", "attachment;filename=" & dt.Rows(0)("Name").ToString())

        Response.BinaryWrite(bytes)

        Response.Flush()

        Response.End()

    End Sub




End Class