createNewFile() throws an error

In my android app I try to create a xml file on sdcard. I tried this :

public class XmlFileCreator extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);


        System.out.println(Environment.getExternalStorageDirectory());
        // create a new file called "new.xml" in the SD card
        File newxmlfile = new File( Environment.getExternalStorageDirectory(),"new.xml");
        try {
            newxmlfile.createNewFile();
        } catch (IOException e) {
            Log.e("IOException", "exception in createNewFile() method");
        }

        FileOutputStream fileos = null;
        try {
            fileos = new FileOutputStream(newxmlfile);
        } catch (FileNotFoundException e) {
            Log.e("FileNotFoundException", "can't create FileOutputStream");
        }
        // we create a XmlSerializer in order to write xml data
        XmlSerializer serializer = Xml.newSerializer();

        try {
            // we set the FileOutputStream as output for the serializer, using
            // UTF-8 encoding
            serializer.setOutput(fileos, "UTF-8");
            // Write <?xml declaration with encoding (if encoding not null) and
            // standalone flag (if standalone not null)
            serializer.startDocument(null, Boolean.valueOf(true));
            // set indentation option
            serializer.setFeature(
                    "http://xmlpull.org/v1/doc/features.html#indent-output",
                    true);
            // start a tag called "root"
            serializer.startTag(null, "root");
            // i indent code just to have a view similar to xml-tree
            serializer.startTag(null, "child1");
            serializer.endTag(null, "child1");
            serializer.startTag(null, "child2");
            // set an attribute called "attribute" with a "value" for <child2>
            serializer.attribute(null, "attribute", "value");
            serializer.endTag(null, "child2");

            serializer.startTag(null, "child3");
            // write some text inside <child3>
            serializer.text("some text inside child3");
            serializer.endTag(null, "child3");

            serializer.endTag(null, "root");
            serializer.endDocument();
            // write xml data into the FileOutputStream
            serializer.flush();
            // finally we close the file stream
            fileos.close();

            System.out.println("file has been created on SD card");         
        }
        catch(Exception e){
            Log.e("Exception","error occurred while creating xml file");
        }
    }
}

but in LogCat I get this :

08-23 11:19:56.776: ERROR/IOException(6333): exception in createNewFile() method
08-23 11:19:56.776: ERROR/FileNotFoundException(6333): can't create FileOutputStream
08-23 11:19:56.776: ERROR/Exception(6333): error occurred while creating xml file

Where is the problem? Why createNewFile() throws an IOException? Need some help, please...

Once check the manifast file that you mentioned the permission to write in external storage or not