Unable to log in to Jabber.org

I’m trying Spark and Jabber for the first time. I set up an account on jabber.org and installed Spark (on Win7 64-bit). When I try to log in to my Jabber account, I just get a user-name-password error. I can log in fine using Psi. All I’m doing is opening Spark, entering my jabber id mjblyth@jabber.org, the password, and jabber.org for the server. Then click login and get the error. Am I missing something?