Build number: 200405251800

File XMIReader contains a code segement:
    public Collection read (InputStream input, 
String uri, RefPackage[] extents, String 
encoding)
        throws IOException, SAXException, 
ParserConfigurationException {            
        InputSource is = new InputSource (input);
        if (encoding != null) {
            is.setEncoding(encoding);
        }
        if (uri != null) {
            is.setSystemId(uri);
            try {
                docURL = new URI (uri).toURL ();
            } catch (URISyntaxException e) {
            } catch (MalformedURLException e) {
            }
            //New start
            catch (IllegalArgumentException e) {
            }
            //New end
        }
        return read (is, extents);
    }

I had to add the line which is enclosed by 
the //New start //New end lines to be able to 
load xmi files.
Otherwise an IllegalArgumentException will be 
thrown.