This wouldn't work if the form is opened and other users then add users. Your data will be out of date. All of this needs to happen when you press OK button.

>I gather that this is a "add user" form?
>if so in the init of the form or the gotfocus of the textbox I would do
>
>Select DISTINCT user_id ;
>from blabla ;
>into array a_user_id
>
>then in the lostfocus or valid of the textbox I would do
>
>ln_ret = ASCAN(a_user_id, this.value)
>if ln_ret <> 0
>return .t.
>else
>messagebox('error',0,'error')
>return .f.
>endif
>
>I think you get the jist of it
>
>Stephen McLaughlin
>"Blastmaster"
>stephenmclaughlin@email.com