After a couple years without problems, suddenly [DenyHosts|http://denyhosts.sourceforge.net/] started blacklisting my own computers when I tried to ssh into the server. I wouldn't even get a chance to login; the ssh connection would just get dropped and that was it.
I've gotten myself blacklisted before (twice) by fat-fingering my password in wrong (twice in a row), but was always able to edit hosts.deny, remove my IP address, and go back to it. This time, when I would restart [DenyHosts|http://denyhosts.sourceforge.net/], my IP would go right back into hosts.deny and lock me back out.
I found [this article|http://www.cyberciti.biz/faq/linux-unix-delete-remove-ip-address-that-d…] which describes the fact that [DenyHosts|http://denyhosts.sourceforge.net/]holds onto IP addresses in multiple places...something I didn't know until now. The technique described there worked perfectly on my [Ubuntu|http://www.ubuntu.com] Jaunty server installation, with one substitution..."/var/lib/denyhosts", in place of the described "/usr/share/denyhosts".