How to get rid of annoying Non-secure Jabber Login popup?

My Messages app out-of-blue started to complain that my GTalk credentials are being sent in non-secured manner.

Your name and password will be sent in a way that is not secure.

Do you still wish to connect to this server?

This was working all the time and I didn't change anything (including my network).

How do I fix it?

I've checked my Server Settings for GTalk account, but it seems my 'Use SSL' is greyed out, so I can't enable it.