Sounds like your school is doing layer-7 filtering, seeing as you get the disconnect message after the logging in message, and not before

Kind of lame really, IRC has real uses too like collaboration on open source - in fact we used it to keep in touch when doing our second year project back at uni

Basically means they're blocking IRC traffic on any port with deep inspection.
If you're lucky though, you might be able to get around it using secure IRC, which is encrypted, so not subject to such advanced filtering

Try "/server irc.calindora.com:+49243" or whatever is required in your irc client to attempt to use an SSL or secure connection instead, where 49243 is our secure SSL IRC port