MAC address? We are not talking about a client-server system here; a database server might keep track keep track of how many users access it, based on IP or MAC, but in the case of VFP, this is responsibility of the operating system.

Some mechanism to control maximum number of users might be desirable; but I think another way must be found.

In the meantime: one mechanism I find interesting is to create a table with 1000 records, and have the executable do something like:

locate for rlock()
if not found() or recno() > MAX_USERS
  MessageBox("Too many users")
  return
endif

Of course, the responsibility of doing this check resides in the executable, and not in the database.