RSS-Feed returns an empty string

I have a news portal that displays RSS Feeds Items. Approximately 50 sources are read and it works very well.

Only with a source I always get an empty string. The RSS Validator of W3C can read the RSS feed. Even my program Vienna receives data.

What can I do?

Here is my simple code:

$link = 'http://blog.bosch-si.com/feed/';$response = file_get_contents($link);if($response !== false) {    var_dump($response);} else {    echo 'Error ';}