We're seeing a lot of people who are using accounts on Google Apps domains having difficulty connecting to the new Partychat services.
If you are using a Google Apps domain, these instructions (from Google) will help you get partychat working again. This will require help from someone with access to your domain settings (probably a system administrator).
If you don't have access to DNS records, or can't find someone who does, you will have to use a @gmail.com account instead.
Every domain needs to have a SRV DNS record to tell other XMPP servers where to connect (if the bare domain does has no record). The SRV record's name should be "_xmpp-server._tcp.domain.com." This doesn't just affect partychat, it prevents most people on non-Google third-party domains from being able to talk to you.
You can check if your server has one by executing the following (change mydomain.com to the name of your domain):
> set q=SRV
** server can't find _xmpp-server._tcp.mydomain.com: NXDOMAIN
As you can see, mydomain.com doesn't have a record, so our servers don't know where to send your chat messages. Here is an example of a properly configured domain:
> set q=SRV
_xmpp-server._tcp.q00p.net service = 5 0 5269 xmpp-server.l.google.com.
_xmpp-server._tcp.q00p.net service = 20 0 5269 xmpp-server1.l.google.com.
_xmpp-server._tcp.q00p.net service = 20 0 5269 xmpp-server2.l.google.com.
_xmpp-server._tcp.q00p.net service = 20 0 5269 xmpp-server3.l.google.com.
_xmpp-server._tcp.q00p.net service = 20 0 5269 xmpp-server4.l.google.com.