sagenb error

joel@joel-laptop:~$ sage
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| Sage Version 5.4.1, Release Date: 2012-11-15                       |
| Type "notebook()" for the browser-based notebook interface.        |
| Type "help()" for help.                                            |
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sage: notebook()
The notebook files are stored in: sage_notebook.sagenb
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* Open your web browser to http://localhost:8080 *
*                                                *
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Executing twistd  --pidfile="sage_notebook.sagenb/sagenb.pid" -ny "sage_notebook.sagenb/twistedconf.tac"
2013-01-20 12:26:15+0100 [-] Log opened.
2013-01-20 12:26:15+0100 [-] twistd 12.1.0 (/usr/lib/sagemath/local/bin/python 2.7.3) starting up.
2013-01-20 12:26:15+0100 [-] reactor class: twisted.internet.epollreactor.EPollReactor.
2013-01-20 12:26:15+0100 [-] QuietSite starting on 8080
2013-01-20 12:26:15+0100 [-] Starting factory <__builtin__.QuietSite instance at 0x54e6ab8>
2013-01-20 12:26:23+0100 [-] WSGI application error
    Traceback (most recent call last):
      File "/usr/lib/sagemath/local/lib/python2.7/site-packages/Twisted-12.1.0-py2.7-linux-x86_64.egg/twisted/python/threadpool.py", line 167, in _worker
        result = context.call(ctx, function, *args, **kwargs)
      File "/usr/lib/sagemath/local/lib/python2.7/site-packages/Twisted-12.1.0-py2.7-linux-x86_64.egg/twisted/python/context.py", line 118, in callWithContext
        return self.currentContext().callWithContext(ctx, func, *args, **kw)
      File "/usr/lib/sagemath/local/lib/python2.7/site-packages/Twisted-12.1.0-py2.7-linux-x86_64.egg/twisted/python/context.py", line 81, in callWithContext
        return func(*args,**kw)
      File "/usr/lib/sagemath/local/lib/python2.7/site-packages/Twisted-12.1.0-py2.7-linux-x86_64.egg/twisted/web/wsgi.py", line 332, in run
        self.reactor.callFromThread(wsgiError, self.started, *exc_info())
    --- <exception caught here> ---
      File "/usr/lib/sagemath/local/lib/python2.7/site-packages/Twisted-12.1.0-py2.7-linux-x86_64.egg/twisted/web/wsgi.py", line 315, in run
        appIterator = self.application(self.environ, self.startResponse)
      File "/usr/lib/sagemath/local/lib/python2.7/site-packages/Flask-0.9-py2.7.egg/flask/app.py", line 1701, in __call__
        return self.wsgi_app(environ, start_response)
      File "/usr/lib/sagemath/local/lib/python2.7/site-packages/Flask-0.9-py2.7.egg/flask/app.py", line 1689, in wsgi_app
        response = self.make_response(self.handle_exception(e))
      File "/usr/lib/sagemath/local/lib/python2.7/site-packages/Flask-0.9-py2.7.egg/flask/app.py", line 1687, in wsgi_app
        response = self.full_dispatch_request()
      File "/usr/lib/sagemath/local/lib/python2.7/site-packages/Flask-0.9-py2.7.egg/flask/app.py", line 1360, in full_dispatch_request
        rv = self.handle_user_exception(e)
      File "/usr/lib/sagemath/local/lib/python2.7/site-packages/Flask-0.9-py2.7.egg/flask/app.py", line 1358, in full_dispatch_request
        rv = self.dispatch_request()
      File "/usr/lib/sagemath/local/lib/python2.7/site-packages/Flask-0.9-py2.7.egg/flask/app.py", line 1344, in dispatch_request
        return self.view_functions[rule.endpoint](**req.view_args)
      File "/usr/lib/sagemath/devel/sagenb/flask_version/decorators.py", line 22, in wrapper
        return f(*args, **kwds)
      File "/usr/lib/sagemath/devel/sagenb/flask_version/worksheet_listing.py", line 68, in home
        return render_worksheet_list(request.args, pub=False, username=username)
      File "/usr/lib/sagemath/devel/sagenb/flask_version/worksheet_listing.py", line 43, in render_worksheet_list
        search=search, reverse=reverse)
      File "/usr/lib/sagemath/devel/sagenb/sagenb/notebook/notebook.py", line 1282, in worksheet_list_for_user
        X = self.get_worksheets_with_viewer(user)
      File "/usr/lib/sagemath/devel/sagenb/sagenb/notebook/notebook.py", line 1460, in get_worksheets_with_viewer
        if self._user_manager.user_is_admin(username): return self.get_all_worksheets()
      File "/usr/lib/sagemath/devel/sagenb/sagenb/notebook/notebook.py", line 1455, in get_all_worksheets
        for w in self.users_worksheets(username):
      File "/usr/lib/sagemath/devel/sagenb/sagenb/notebook/notebook.py", line 372, in users_worksheets
        worksheets = self.__storage.worksheets(username)
      File "/usr/lib/sagemath/devel/sagenb/sagenb/storage/filesystem_storage.py", line 600, in worksheets
        path = self._abspath(self._user_path(username))
      File "/usr/lib/sagemath/devel/sagenb/sagenb/storage/filesystem_storage.py", line 119, in _user_path
        os.rename(path, new_path)
    exceptions.OSError: [Errno 39] Directory not empty