> Unfortunately, CLOSE ALL is spread throughout the code of
> all the programs so using a low level file open/create to
> make a file that only exists during execution of the program
> won't work. This is the method I've used in the past.

How about creating a permanent DBF? Every time a user logged
in, a record is inserted into it; logout, removed from it.
A look into the table will know who is/are using a program,
what program, when... Then you can control access.