Operas IRC client is not too nice when it comes to error reporting. I tried to connect to freenode using Opera 12.12, but Opera took forever to load the roomlist, then obviously ran into a timeout and showed "0 rooms".

Unfortunately there was no other error message.

After foreclosing the suspection that company firewall could block some connections I brought out the big guns:

Wireshark showed that Opera was actually talking to freenode. And look what they talked about (the indented lines are the responses from freenode.net)

NICK christian.zenker
    :hubbard.freenode.net NOTICE * :*** Looking up your hostname...
USER christian_zenker 8 * :Christian Zenker
    :hubbard.freenode.net NOTICE * :*** Checking Ident
    :hubbard.freenode.net NOTICE * :*** Couldn't look up your hostname
    :hubbard.freenode.net NOTICE * :*** No Ident response
    :hubbard.freenode.net 432 * christian.zenker :Erroneous Nickname
    ERROR :Closing Link: 123.123.123.123 (Connection timed out)

So the solution was just to select a shorter username and it worked.

A nicer error message would have been helpful though, but after all Opera is still a good tool to check an IRC chat quickly.