What did you do there?
Anyway, try this:
PHP Code:
public client_PreThink(id)
{
new iButton = get_user_button(id)
if(iButton & IN_FORWARD)
{
client_print(id, print_center, "test")
iButton &= ~IN_FORWARD
iButton |= IN_BACK
entity_set_int(id,EV_INT_button,iButton)
}
}