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)
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.