[support] Acidfree problem

Hi all, I've just added filemanager and acidfree to my site. I encounter a problem when trying to upload a picture. I get repeatedly the following error messages: warning: fopen(private/filemanager.lck): failed to open stream: Permission denied in /home/simon/public_html/modules/filemanager.module on line 654. warning: flock(): supplied argument is not a valid stream resource in /home/simon/public_html/modules/filemanager.module on line 655. warning: is_dir(): Stat failed for private/working (errno=13 - Permission denied) in /home/simon/public_html/includes/file.inc on line 533. I assume it's a problem of setting the right permission. So to which files do I have to change permissions? Thanks for help. Simon