Keep Pidgin up to date

If your pidgin IM fails to connect to ICQ, you may need to update it. The ubuntu default sources are usually outdated.

Just follow the instructions 1-4 and 1-3 on the page linked below.

Making SSL connection work

If you can not connect using SSL, open up the account settings and enable "clientLogin". Also, your Server should be set to slogin.icq.com.