Fatal error: Call to a member function theme() and menu navigation not working

So lately i have uploaded my wordpress to 4.0, i thought was all fine up till today when i also had to update my downloaded theme: radiate.

I’ve got multiple errors which i don’t know how to fix, hence me asking the question in here. These multiple problems may somehow be connected with each other though.

1. The first problem i encountered was that my navigation to the menus isn’t working correctly anymore. When i navigate to a menu item (or a sub menu item) it just wont go to the page but instead it stays on the home page. Though, the link is changing (www.mysite.com/The_menu_I_clicked).

2. When i try’d to go to the pages menu in the admin i noticed something else, the menu that is usually on the right side (where you can set public, private, password, etc.) is gone… there is only a square which is dashed (see this image: Link to my error / square).

3. When i try to go and customize my theme in the admin i get the following error: Fatal error: Call to a member function theme() on a non-object in /home/deb11421/domains/marceldepender.nl/public_html/Recap/wp-admin/customize.php on line 88

4. When i try to go to the header or background menus in the admin i get the following error: You do not have sufficient permissions to access this page.

I didn’t have had any of these problems before the wordpress/radiate theme updates.. anyone knows what is causing this? I also try’d to install a new www.remarpro.com application with a different site name and theme but here the problems are the same..