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All who has webspace at Host Europe and installed WordPress by itself (not out of the box) have problems to use the autoupdate function from WordPress.

For me it said always that the installtion path of WordPress was not found. Now, after a long while, I found a german blog article WordPress AutoUpdate bei Hosteurope. There is described that you just have to put one single line in the config file wp-config.php of WordPress and all works as expected. The problem which cause the error is the directory for temporary files, which is set by this line via a environmental variable.

putenv('TMPDIR='.ini_get('upload_tmp_dir') );
if ( !defined('ABSPATH') )
   define('ABSPATH', dirname(__FILE__) . '/');

Just put the bold line in your config-file at this position and then you can use WordPress auto update. But be sure to backup your data as explained in the WordPress Codex!