Trouble parsing some RSS feeds using Java and Sax

Question

I've written an RSS feed parser in Java (running on Android) and it parses some feeds perfectly, and others not at all. I get the following error when it tries to parse Slashdot (http://rss.slashdot.org/Slashdot/slashdot)

org.apache.harmony.xml.ExpatParser$ParseException: At line 1, column 0: unbound prefix

If I try to parse Wired (http://feeds.wired.com/wired/index)

org.apache.harmony.xml.ExpatParser$ParseException: At line 1, column 0: syntax error

If I try to parse AndroidGuys (http://feeds.feedburner.com/androidguyscom)

org.apache.harmony.xml.ExpatParser$ParseException: At line 1, column 0: syntax error

Here is some code for my parser.

public void updateArticles(Context ctx, Feed feed, int numDaysToGet) {
    try {
        targetFlag = TARGET_ARTICLES;
        tweetDB = new TweetMonsterDBAdapter(ctx);
        tweetDB.open();
        currentFeed = feed;
        TimeZone.setDefault(TimeZone.getTimeZone("UTC"));  // or "Etc/GMT-1"

        Date currentDate = new Date();
        long dateInMillis = currentDate.getTime();
        oldestDate.setTime(dateInMillis-(dayInMillis*numDaysToGet));

        SAXParserFactory spf = SAXParserFactory.newInstance();
        SAXParser sp = spf.newSAXParser();
        XMLReader xr = sp.getXMLReader();
        xr.setContentHandler(this);
        xr.parse(new InputSource(currentFeed.url.openStream()));

    } catch (IOException e) {
        Log.e("TweetMonster", e.toString());
    } catch (SAXException e) {
        tweetDB.close();
        Log.e("TweetMonster", e.toString());
    } catch (ParserConfigurationException e) {
        Log.e("TweetMonster", e.toString());
    }
    tweetDB.close();
}

It doesn't even get into my startElement method.