Thanks for your answer.
I had copied the error console below my message.
It took three TB restarts to get back my original agenda.
The problem : all the contacts were doubled, repeated twice !?
One more restart, and got back finally to original configuration.
It was a real nightmare for a while.
I hope this time, it will remain as it is.
Question : is there a way to check a TB update will not cause such a mess, before actually updatind TB ?
Thanks in advance for your answer.