Many of you in recent weeks have probably faced problems with Facebook XMPP's server. They are migrating to new servers which have had their share of problems, causing KDE Telepathy clients to display the following:
Not everyone is affected at the same time due to a gradual roll out by Facebook.
This particular problem is caused by a non RFC compliance in Facebooks XMPP service.
I don't mean to blame the Facebook developers here, everyone makes mistakes, especially when dealing with XMPP :)
In this particular case they are missing a parameter which, whilst required by the specification, is not practically needed. Our library then assumes something is wrong and quits.
Thanks to help from users at http://forum.kde.org I was able to reproduce the problem.
I have added a workaround in the Telepathy Gabble backend to resolve this issue which should fix KTp, Empathy, and other Telepathy users (including the Nokia N9 if they were to make a new release). Other upstream developers helped spring into action to clarify RFCs, add regression tests and backport into 3 different stable releases.
It really highlights the importance and advantages of sharing backends.
In order to prevent problems like this in the future I am now a member of the Facebook XMPP developer relations group. In addition I now connect to a beta version of the Facebook Chat gateway so we can spot and communicate errors faster.
Upgrade telepathy gabble to the latest version (0.18.1) and this problem should go away. Backports are coming soon.