If you are receiving the error that reads "Connection error when attempting to authenticate your account(2)":

In Windows, go to the Start->Run box and put this in exactly:
"C:\Program Files\Trillian\trillian.exe" /showmemberlogin nossl
(this is assuming your install of Trillian is in the default location. If yours is different, point to your install and then do the /showmemberlogin part)

When the membership information box opens, click the "Proxy Setup" button and make sure your proxy information is correct. (By "correct" that if you don't use a proxy, the box is UNchecked. If you do use a proxy, that the box is checked and the proper information is entered in the fields.)

If you are receiving the error that reads "Connection error when attempting to authenticate your account(6)":

Launch Internet Explorer, go to the File menu and UNcheck "Work Offline". Restart Trillian Pro.