[Zope] Can't connect to Zope server when there is no internet connection...

Hello, I’m running Zope 2.5.1 with Python 2.2 on Win2k. When I'm connected to the Internet (eg via modem and phone line), I can happily access my Zope server. However, when there is no connection available, IE 5.5 won't connect to Zope. Is there any idea what could go wrong? Lars