Netinfo crashes and makes OWA unusable

We run Microsoft Exchange 5.5 under Windows NT 4.0. Whenever anyone uses Outlook Web Access on any browser, on or off our LAN, it crashes netinfo and aborts the FTP and World Wide Web publishing services. It authenticates fine, but as soon as the user reaches a mailbox, opens an email and tries to answer or forward it, FTP and Web Publishing shut down and a Dr. Watson message appears on the server about Netinfo. This still happens even though our integrator has de-installed and re-installed IISand OWA. Suggestions, anyone?