Netinfo crashes OWA

We run Microsoft Exchange 5.5 under Windows NT 4.0. Here’s our problem: When any user goes to Outlook Web Access on any browser from any computer, on or off our LAN, it authenticates fine, but as soon as (s)he reaches a mailbox, opens an email and tries to answer, delete or forward it, that aborts FTP and Web Publishing and a Dr. Watson message appears saying that Netinfo has failed. Our integrator has removed and re-installed OWA and IIS to no avail. What to do?