Issues after WordPress 3.5.1 upgrading

I had 3.5 version, and it worked fine. Today I upgraded to 3.5.1 version, but after installing it, even if installation worked fine, I’m experiencing some issues:
– In may home page, I can see the following error: Fatal error: Call to undefined function dynamic_sidebar() in /home/mhd-01/www.bartfoto.it/htdocs/wp-content/themes/elastico/sidebar.php on line 47 (and the sidebar is not showing)
– In Appearance – Widgets, I can see available widgets, but in the “Inactive widgets” part of screen, I have the following: “Drag widgets here to remove them from the sidebar but keep their settings.
Fatal error: Call to undefined function dynamic_sidebar() in /home/mhd-01/www.bartfoto.it/htdocs/wp-admin/includes/widgets.php on line 80″

The drag&drop in this page is not working.

I also updated following plugins, but I didn’t check if the blog was fine before plugin updates…
– Better WP Security (3.4.7)
– Contact Form 7 (3.3.3)
– Ultimate tag cloud widget (2.1)
– Widgetize pages Light (1.5)

I’ve the “Elastico” plugin, that is not supported yet ??
My website is: https://www.bartfoto.it