Hi,
when a new user mistypes his registration code, a
traceback message is shown instead of a user-friendly
error message.
To reproduce, browse an url like
http://yourhost/cgi-bin/roundup.cgi/yourtracker/?@action=confrego&otk=any_old_thing

This bug is also submitted in the Debian bug tracking
system at
http://bugs.debian.org/228287

Oh, just saw in 0.7 changelog that replying to
new-registration mails works now, so this is more a
feature/wishlist thing :)