The only other google result for that error message brings up a Debian bug report from December 2008. Since Ubuntu uses Debian's packages, it's decently likely that the version of libsoap-lite-perl you're using has the same broken behavior.
You can try either updating the SOAP::Transport::HTTP::Apache package directly through CPAN, or modify the file as suggested in the report. For me, on CentOS 5, it's at /usr/lib/perl5/vendor_perl/5.8.8/SOAP/Transport/HTTP.pm, at line 647 (although, of course, differing versions may change that quite a bit). It's worth noting that mine also has the original line (without HTTP_BAD_REQUEST), so if neccessary, I can try to go through the Moodle process myself and play around with things.
If this does indeed fix it, we should probably report this upstream, if it hasn't been already.
HTH.