GREAT me too, now...
I am unable to log into admin along with the inability to log in through the front end as well.
Joomla 1.6.+
Newest CB and UddeIM
It was working fine for a while, then the front end gave this error.
Soon after, the backend simply reloads the blank login form and wont let me in.
Session expired or cookies are not enabled in your browser...
This is what we see on the front end.
Newest IE9, Firefox and my own personally made web browsers give same result.
Any suggestions??
I may go back to the old Joomla and CB if there's no progress here, and my case seems the most difficult without a backend login ability. But yeah, WHY IS this going on?? It DID work GREAT for a while!!
(addendum)
I did read this for those who CAN get into back-end yet...
Go to CB > Configuration > Integration
The second field is labeled: "Enable anti-spoofing sessions checks". TURN THIS OFF!!! (set to "No").