Hi Robert Kavgić,
I’ve already trying to add this solution in .htaccess but the problem persists… :/
I don’t know, but could be the server of the client, it uses Windows, not Linux.
Maybe this could be the problem?
I’ll try to contact the hosting server to ask for migration to know if it can be, not even the Contact Form 7 is running the file upload, saying it’s the server’s block and couldn’t save. I’ve try to add this line in “wp-config.php” but with no sucess too.