When trying to view my attached file I received error pasted below. The
fix was easy (once found) to make sure the header Content-Length got as
value a string instead of a long. 
On line 1326 mane sure you cast to string:
self.setHeader("Content-Length", str(length))

Error:
[Fri Oct 16 06:47:30 2009] [error] [client 85.91.175.212] mod_wsgi
(pid=8183): Exception occurred processing WSGI script
'/var/www/djagios.org/roundup/roundup.wsgi'., referer:
http://tracker.djagios.org/issue2
[Fri Oct 16 06:47:30 2009] [error] [client 85.91.175.212] Traceback
(most recent call last):, referer: http://tracker.djagios.org/issue2
[Fri Oct 16 06:47:30 2009] [error] [client 85.91.175.212] File
"//usr/lib/python2.5/site-packages/roundup/cgi/wsgi_handler.py", line
58, in __call__, referer: http://tracker.djagios.org/issue2
[Fri Oct 16 06:47:30 2009] [error] [client 85.91.175.212] client.main(),
referer: http://tracker.djagios.org/issue2
[Fri Oct 16 06:47:30 2009] [error] [client 85.91.175.212] File
"//usr/lib/python2.5/site-packages/roundup/cgi/client.py", line 361, in
main, referer: http://tracker.djagios.org/issue2
[Fri Oct 16 06:47:30 2009] [error] [client 85.91.175.212]
self.inner_main(), referer: http://tracker.djagios.org/issue2
[Fri Oct 16 06:47:30 2009] [error] [client 85.91.175.212] File
"//usr/lib/python2.5/site-packages/roundup/cgi/client.py", line 523, in
inner_main, referer: http://tracker.djagios.org/issue2
[Fri Oct 16 06:47:30 2009] [error] [client 85.91.175.212] return
self.write_html(self._(error_message)), referer:
http://tracker.djagios.org/issue2
[Fri Oct 16 06:47:30 2009] [error] [client 85.91.175.212] File
"//usr/lib/python2.5/site-packages/roundup/cgi/client.py", line 1124, in
write_html, referer: http://tracker.djagios.org/issue2
[Fri Oct 16 06:47:30 2009] [error] [client 85.91.175.212]
self._socket_op(self.request.wfile.write, content), referer:
http://tracker.djagios.org/issue2
[Fri Oct 16 06:47:30 2009] [error] [client 85.91.175.212] File
"//usr/lib/python2.5/site-packages/roundup/cgi/client.py", line 1081, in
_socket_op, referer: http://tracker.djagios.org/issue2
[Fri Oct 16 06:47:30 2009] [error] [client 85.91.175.212] call(*args,
**kwargs), referer: http://tracker.djagios.org/issue2
[Fri Oct 16 06:47:30 2009] [error] [client 85.91.175.212] TypeError:
expected string object for header value, referer:
http://tracker.djagios.org/issue2

Thanks for this report. It was fixed a while ago but I didn't close this issue.