WinExec does not start application

here the code I use for the select box and the aplication to run.

//
// Execute *.plt files
//
void TFEMWorkMDIClient::CmExecutePlt()
{
      FileData.Flags = OFN_FILEMUSTEXIST|OFN_HIDEREADONLY|OFN_OVERWRITEPROMPT|
                    OFN_SHAREAWARE;
   FileData.SetFilter("GNUPlot Files (*.plt)|*.plt|All Files (*.*)|*.*|");
   FileData.InitialDir = (char *)Settings.DataPath.c_str();

   int but = TFileOpenDialog(GetApplication()->MainWindow, FileData).Execute();
   if(but==IDOK)
   {
      string cmdLine;
      string msgBoxTitle;
      string msgBoxText;

      // cmdLine = "C:\\Progra~1\\Gnuplot\\WGnuplot.exe ";
      cmdLine = Settings.PlotPath + Settings.PlotApp;
      cmdLine += " "; // separator
      cmdLine += FileData.FileName;

      int   result = WinExec(cmdLine.c_str(), SW_SHOWNORMAL);
      if((result>=0)&&(result<=32))
      {
         switch (result)
         {
            case 0:  msgBoxTitle = "ERROR: Out of memory"; break;
            case 2:  msgBoxTitle = "ERROR: File not found"; break;
            case 3:  msgBoxTitle = "ERROR: Path not found"; break;
            default: msgBoxTitle = "ERROR: Error in WinExec"; break;
         }
         msgBoxText = "Command line:\n";
         msgBoxText += cmdLine;
         ::MessageBox(GetActiveWindow(), msgBoxText.c_str(), msgBoxTitle.c_str(), MB_OK);
      }
   }
}

//
// Run the GNU Plot for Profile
//
void TFEMWorkMDIClient::CmAnimProfTemp()
{
   int   but=::MessageBox(GetActiveWindow(),
                          "Animate Temperature Profile?",
                          "Run GNUPlot", MB_OKCANCEL);

   if(but==IDOK)
   {
      string cmdLine;
      string msgBoxTitle;
      string msgBoxText;

      // cmdLine = "C:\\Progra~1\\Gnuplot\\WGnuplot.exe data\\TempSimu.plt";
      cmdLine = Settings.PlotPath + Settings.PlotApp;
      cmdLine += " "; // separator
      cmdLine += Settings.MeshPltPath + "TempSimu.plt";

      int   result = WinExec(cmdLine.c_str(), SW_SHOWNORMAL);
      if((result>=0)&&(result<=32))
      {
         switch (result)
         {
            case 0:  msgBoxTitle = "ERROR: Out of memory"; break;
            case 2:  msgBoxTitle = "ERROR: File not found"; break;
            case 3:  msgBoxTitle = "ERROR: Path not found"; break;
            default: msgBoxTitle = "ERROR: Error in WinExec"; break;
         }
         msgBoxText = "Command line:\n";
         msgBoxText += cmdLine;
         ::MessageBox(GetActiveWindow(), msgBoxText.c_str(), msgBoxTitle.c_str(), MB_OK);
      }
   }
}