I/O Error 103 Attempting to Reach an HTTP Server

We've been getting an error "I/O Error 103" attempting to reach an HTTP
server.  At first we thought this was some problem relating to Delphi 6's
Web Services, but we've now seen it attempting to reach an Indy HTTP server
from an Indy HTTP client.  The appearance of the problem is unpredictable --
sometimes everything works fine, other times we can't get a connection at
all.  The only hint we have is that the problem never seems to occur when
we're trying to reach the server on an internal network, only when we're
attempting to work across a WAN.  Can anyone shed some light on this?  TIA.