If you're having trouble connecting on ICQ using Trillian, there's a file that needs to be replaced.
The file is found in
C:\Program Files\Trillian\Plugins
Exit Trillian, Navigate to the appropriate folder above, and replace the aim.dll file with the one in this zip file. The restart trillian and it should connect to ICQ.
The file can be found here:
http://forums.ceruleanstudios.com/attachment.php?attachmentid=22790&d=1247588823