You don't have permission to access /wp-admin on this server.

Site suddenly did not like me – error message. I had been trying to update WP3.1.2 automatically to wp 3.1.3 but got a “can’t write” error. Then tried to update a plugin automatically, locked up.
So… being either brave or stupid I did a manual update – kept the contents folder, plus wp-config.php and .htaccess.
Still does not like me.
On the way to this point I found I could not log in to other sites of this installation, then the big message for the main site – You don’t have permission to access /wp-admin on this server.

Maybe it has something to do with the retained contents folder…

Any ideas?