Here is a link to a thread on the Computers BBS talking about the 4chan ban error:
http://dis.4chan.org/read/comp/1327064370/1-40
Apparently, a lot of people are having this problem.
"There was no entry in our database for your ban. Therefore, the reason for this ban cannot be automatically determined. It is likely that your ISP is caching a ban intended for someone else. Please contact a moderator on #4chan @ irc.rizon.net with your IP address (IP adress) for more details. Moderators are channel ops (@) and half-ops (%)."