My server doesn't return the ASCII or HTML responses, but all the others (DAS, ..., Info) work fine.
The ASCII and HTML responses are generated by accessing the server using the URL (a future version of the server may use a different design; this is true for version 3.4 and may be true for some later versions). If you are serving data behind a firewall which uses NAT for address traslation, the DNS lookup for the host name can fail.
Greg Miller from the USGS tracked down this problem and came up with a solution:
I am behind a firewall that uses NAT translation, so if it was relying on DNS to find the address, it would fail. I checked my host file and discovered that Red Hat maps the server name into the loopback address and not the IP address of the ethernet interface. I corrected the host file, and everything works fine.