Hi Mathew.

Take the MessageBox out of your main program and move it to the IsAppRunning Function like to:

IF lnHWND > 0
  *** We have found something!
  MESSAGEBOX( "Only one instance of this application can be run at a time.", 64, lcTitle )

  *** So make it uppermost and maximize it (ShowWin => 3)
  BringWindowToTop( lnHWND )
  ShowWindow( lnHWND, 3 )
  *** Set the Return Value
  llRetVal = .T.
ENDIF