>I have execute file call ac.exe, I want to make this exe only single user can use . How to make exe to single user environment . In login form ie ok button and cancel button. In ok button, I do set the public
>variable multi_user to "N" as belows:-
>
>Multi_user = "N"
>then In the Ok Button check :-
> If Multi_user ="N"
> set exclusive on
> else
> set exclusive off
> endi
>
>I test run, Two persons still can get in
>then i try the other ways. I put same code into the Main.prg, Well I works. It come out the message : Access Denied. But the problem the message box have three buttons ie cancel, ignore, help. I try to click ignore... It let me into the program.... Why

Just because you SET EXCLUSIVE ON does not mean that two people cannot run the program at the same time. You will not get a collision until one or the other tries to use a table that is already in use.

If there is a shared drive where the data resides, you could write a file out that indicates the user is logged in, or lock a record in a table (logon.dbf) in your app and deny access to anyone else when they attempt to log in.

HTH