>I don´t have. My idea is, when a user wants to update a table and that table is being used by another user, I want to know who is the other user and show a message "The user XXXX is using the file" or something like that, but I don´t know how.

Not sure, if this still works, but you may try Who opened what files on the network? (modified to use only VFP code) FAQ #7896