@Styled Themes, Thanks for the advice. Dispite the search and answers it did not fix the problem. I already had the permissions of all folders on 777. I also tried 755 or 666, but nothing solved the problem. I did this on de folder wp-content, including its sub-folders. And later on I also did this on all folders. Do you have an other solution? Thanks.
I would recommend posting this in the support forums at wordpress.org and see what others suggest. You may also want to contact your host support to see if they can find the issue because it does look look like a permissions problem which may be server side (on the web host).
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