You are unable to upgrade automatically your WordPress installation. You are also not able to update your plugins. You have also tried everything to make your connection settings correct and it still does not work.
The reason: Your PHP scripts does not have the permission to write.
The solution: Install suPHP
$ apt-get install libapache2-mod-suphp
Add this in your Apache conf:
$ a2dismod php5 $ /etc/init.d/apache2 restart
CHOWN and CHGRP your home directory
$ chmod -R wenbert /home/wenbert $ chgrp -R wenbert /home/wenbert
FYI: I am on Ubuntu.