I’ve been having the same identical problem and have been told to check a number of things but nothing seems to work. If you come across anything please let me know and I’ll do the same.
I will copy and paste the main suggestions for you here, after I find the post.
Thanks
Here is what was suggested for this problem.
First you can see if this is caused by a plugin by using your FTP client to rename your wp-content/plugins directory temporarily.
Second you can look at your admin login to ensure it still has the admin capabilities –
Access your database via phpMyAdmin (most hosting providers offer this in their control panel), go to the wp_users table and find the row for your user_login . Note the ID of this row. Now, go to the wp_usermeta table and find the wp_capabilities row for your user_id . Set the value of this row to a:1:{s:13:”administrator”;b:1;}