cannot save picture

Hi, I think, I have installed WP correctly in a DEBIAN environment. On server side, the whole /wp directory is owned by the user, which I configured to be wordpress admin. The whole wp-directory tree has “rwx” rights to the wordpress admin.

However, when I try to install the header picture in my theme, I see the error: cannot create wp-content/uploads/2015/01. Maybe the directory above is not writeable

“Das Verzeichnis wp-content/uploads/2015/01 kann nicht angelegt werden. Ist das übergeordnete Verzeichnis durch den Server beschreibbar?”

ANY IDEA?