E_ERROR - Call to a member function set() on a non-object after upgrade

i get this message after the upgrade of the latest version why???

Server Error
Sorry, something went terribly wrong!

E_ERROR - Call to a member function set() on a non-object

For further details please review your logs/ folder, or enable displaying of errors in your system configuration.

Hi Sotiris, can you turn on errors.display: true (http://learn.getgrav.org/basics/grav-configuration )? I think this is related to http://getgrav.org/forum#!/installation-configuratio:call-to-a-member-function-s . If that's the same problem try composer update in the grav root.