Hi Georges,
Just for the record, i just have the same issue with a new site.
The site was developped on a first domain, all working fine.
When the site went to be active, the frontend works fine but the backend show the error for every part of Flexicontent.
To put the site active, i did this : i aim the new domain to the same folder on the server.
Anyway, i emptied the template table on phpmyadmin and all thing go back to normal : i have a message with "flexicontent corrections to do : fix initial permission".
When done, i have the correct access to content and all FC.
The only thing : my fields in template have to be put in place again. I find the defaults of the first install (i think FC put the defaults when the table is emptied ?). I drag my fields in the render only space, remove the fields i dont want and all is ok.
If that can help
By the way, i use the very last one available version : 2.2.1RC
Have a nice day !
Xavier