Sometimes "Premature end of file"

When loading the url http://www.swr.de/blog/swr1_rp/feed/rss/ sometimes an exception is thrown:

com.sun.syndication.io.ParsingFeedException: Invalid XML: Error on line -1: Premature end of file.
at com.sun.syndication.io.WireFeedInput.build(WireFeedInput.java:198)
at com.sun.syndication.io.SyndFeedInput.build(SyndFeedInput.java:123)

We use this code:

SyndFeedInput input = new SyndFeedInput();
feed = input.build(new XmlReader(new URL(url)));

This doesn't happen on every machine. On a local tomcat, it works, on an different server not. But it works, if I try to debug the code when I connect via a remote debugger, so i can't debug it.