StackTrace returns nothing

Question

We are having a windows service, which download files from an FTP location. If there is an exception we are sending email

But StackTrace returns nothing.

 public void Send_Mail(string strTitle, Exception ex, string MsgSubject)
        {

            System.Diagnostics.StackTrace StackTrace = new System.Diagnostics.StackTrace(ex,true);
            StringBuilder msgBody = null;
            msgBody = new StringBuilder();
            msgBody.Append(ex.Message);
            try
            {
                if (StackTrace.FrameCount > 0)
                {
                    foreach (StackFrame r in StackTrace.GetFrames())
                    {
                        msgBody.Append(String.Format("Filename: {0} Line: {1} Column: {2} Offset: {3} Method: {4} <br/> ",
                            r.GetFileName(), r.GetFileLineNumber(), r.GetFileColumnNumber(), r.GetILOffset(), r.GetMethod()));
                    }
                }
            }
            catch (Exception exMail)
            {

            }
            finally
            {

            }
        }