Same problem while upgrading my site on Enterprise open source softtare.
The “clear private datas” trick did not work.
The problem was that I did not desactivate plugins.
To solve the problem in in such cases:
– Connect to your database ( via PhpMyAdmin for example)
– Find the wp_options->active_plugins row
– Edit it, and put:
a:0:{}
in that row.
Solved the problem for me.
