Connection to Informix

I'm working with PowerBuilder 4.0 and Informix 7.4 (?). I have a dialog box when the user have to type his login and his password and press an accept button. Then, the login and the password in the sqlca are setted with the values of the fields in the dialog, and try the connection. If the values are rigth, the connection work. If the values are incorrects the connection is refused. However, if happen this, when the user try to connect again with the right values, is imposible establish the connection. Only when the engine is restarted is posible connect again to the server. Somebody know what happen here? jmolina