>George,
>
>Even the 2nd, 3rd etc instances of the program GetLastError() returns 0.
>
>Have I set the thing up correctly? If so, must this all be done from a form not the main.prg?
>
>TIA
Mike,

You can store the class in a prg or vcx. The methods shown in the article (Init, Destroy and DisplayInstance) I think are all you need. In your main program, you should have code like this.

lcformcaption = _SCREEN.Caption
_SCREEN.Caption = ""
* Use only one of the next two lines.
SET PROCEDURE TO Mutex ADDITIVE && if in a prg
SET CLASSLIB TO Mutex ADDITIVE && if in a VCX
oMutex = CREATEOBJECT('Mutex', lcformcaption)
IF oMutex.nMutexErr # ERROR_ALREADY_EXISTS
  * Your normal setup code here. (DO MYMENU.MPR, READ EVENTS, etc.)
ELSE
  * If we hit this line, the other instance is displayed
  * and the current one released
  oMutex.DisplayInstance
ENDIF

Does this help?