Broken Pipe errors with dialup users

We are experiencing an intermittant problem where dial-up users that access our customers web servers through our Sprint NAP connection get "broken pipe" errors. This problem seems to appear with a greater frequency with users that use Apple Macintoshs with MacTCP, although Win95 users have also complained of the same problem. With the Win95 users they can change their local MTU setting to 1500 and the problem disappears. We are connected to the Sprint NAP via a full duplex Fddi PA on a Cisco 7505. Anyone encountered this type of problem before? Any thoughts would be greatly appreciated. Off I go to dig into the packets and start testing :) Thanks, Mark Tripod Senior Backbone Engineer Exodus Communications