Problems running a .Net executable from Task Scheduler, program uses Process.Start

I have a Windows Forms Program, C#, that does a lot of preliminary work and then wants to launch another exe.  This works perfectly when run "normally".  However, when run from Task Scheduler, the called program does not appear to start up.  I guess my question is "what is the difference between double-clicking on the exe and starting it from Task Scheduler?"  In both cases, we are administrator with full privileges.  Because we are on a 64-bit machine we have tried compiling specifically as x64 to see if Task Scheduler liked that better, but it did not work.  Thanks.

        private bool PostOrders()
        {
            DateTime pDate = DateTime.Now.Date;

            try
            {
                string FJParam1;
                string FJParam2;
                string FJParam3;

                FJParam1 = "OE03S3  OEOEMENUYYYP                    ";

                FJParam2 = this._Machine.PadRight(20);

                FJParam3 = (this._DB + this._User.Trim()).PadRight(20);

                string ErrMsg = "";
                string rootDir = "";
                rootDir = this.RootFolder(ref ErrMsg);


                if (ErrMsg.Trim().Length != 0)
                {
                    throw new Exception("Finding Root Folder: " + ErrMsg);
                }
                Directory.SetCurrentDirectory(rootDir);


                Process post = new Process();
                ProcessStartInfo psi = new ProcessStartInfo();


                psi.UseShellExecute = false;
                psi.CreateNoWindow = false;
                psi.FileName = rootDir + @"\TargetProgram.EXE";
                psi.Arguments = FJParam1 + FJParam2 + FJParam3;
                psi.Domain = this._Domain;
                psi.UserName = this._UserName;
                SecureString pwd = new SecureString();
                pwd.AppendChar('P');
                pwd.AppendChar('a');
                pwd.AppendChar('s');
                pwd.AppendChar('s');
                pwd.AppendChar('W');
                pwd.AppendChar('o');
                pwd.AppendChar('r');
                pwd.AppendChar('d');


                psi.Password = pwd;

                using (post = Process.Start(psi))
                {
                    post.WaitForExit();
                }


                return true;
            }
            catch (Exception ex)
            {
                throw new Exception("At PostOrders: " + ex.Message);
            }
        }