In order to have this issue solved both with automatic WordPress upgrades or plugin installations you will have to open the .htaccess file in the root of your wordpress installation and add the following line at the bottom of the .htaccess file:
* AddType x-mapp-php5 .php
After you have added this to your .htaccess file upload it to your webserver and refresh the admin screen. Now you will be able to download and install plugins and WordPress upgrades again using the web interface.
