1. The capability upload_files is checked so that won’t be the problem.
2. I’ve got several plugins to restrict access to the backend. But when I de-activate them it still won’t work unfortunately.
I use the following plugins:
Category Posts Widget
Contact Form 7
Frontier Post
Select Frontier Restrict Media
Google Analytics
Google Sitemap by BestWebSoft
Login With Ajax
Page Links To
Peter’s Login Redirect
Remove Dashboard Access
Restrict Widgets
SG CachePress
SI CAPTCHA Anti-Spam
User Role Editor
WordPress SEO