WebGUI

Hello! I have a problems with WebGUI. Locally it works. But I can't logon to system via internet. Logon page simply refreshes. If I set login and password in webgui service properties in tcode SICF it works. SAPLOCALHOSTFULL and icm/host_full_name are set to 'sap.<xxx>.ru' (external address wich ISA redirects to local SAP host). I think that problem is in the incorrect cookie, because with HttpLiveHeader utility i see that string 'set_cookie... domain=.<xxx>.local', but I have no idea where from this local domain name. Help me please!!!