Access Author-Role to upload

Hello,
on my site the users are able to create own posts. Unfortunatelly the upload of images wont work.
Everytime i get the Error:
"Sorry, you are not allowed to attach files to this post."

I dont want the users to edit others posts. Codepart of the causing error is
#: wp-admin/includes/ajax-actions.php:2079
At the moment i removed (commended out) the part of code, but its no solution for long and i hate to work in the core files.

Following solutions i already tried but doesnt work:
1.

$user_role = 'author';
$contributor = get_role($user_role);
$contributor->add_cap('upload_files');

2. Plugin “User Role Editor”

Hope you can help me!
Thanks in advance

• This topic was modified 8 years, 10 months ago by firehold.
• This topic was modified 8 years, 10 months ago by firehold.