Quite understandable, given the lack of clearness on what to do.
Unfortunately, this makes it impossible for the client to respond
appropriately (with something like "This document is only available in
formats I do not understand. Woud you like to download it anyway?", ideally
enumerating which formats it *is* available in and allowing the user to
choose one.)
In the meanwhile, let me guess, it responds with those famous words,
"The information server either is not accessible or is refusing to serve the
document to you." :-)
-- Marc VanHeyningen <http://www.cs.indiana.edu/hyplan/mvanheyn.html>