Running SAGE notebook files across multiple platforms via Dropbox

edit

Hi: this is a kind of follow-up to http://ask.sagemath.org/question/1576.... I have two Mac OS X 10.6.8 computers on which I have just installed SAGE v5.7. I have followed the accepted instructions on the above link and it all works fine on machine1, but when I go to run it on machine2 (irrespective of whether it is or is not still running on machine1) I get the screed of errors reproduced below (sorry but my low karma won't allow me to upload the file ...). Since I would like also to use this Dropbox facility on my university HP notebook with Windows 7 (using VM) I would love to know what basic step is missing from what I am doing, so that hopefully I can get it to work across all platforms smoothly.

Any help would be great thanks!!

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| Sage Version 5.7, Release Date: 2013-02-19                         |
| 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"
2013-02-25 08:40:26+0000 [-] Log opened.
2013-02-25 08:40:26+0000 [-] twistd 12.3.0 (/Applications/sage/local/bin/python 2.7.3) starting up.
2013-02-25 08:40:26+0000 [-] reactor class: twisted.internet.selectreactor.SelectReactor.
2013-02-25 08:40:26+0000 [-] QuietSite starting on 8080
2013-02-25 08:40:26+0000 [-] Starting factory <__builtin__.QuietSite instance at 0x10d5590e0>
2013-02-25 08:40:26+0000 [-] WSGI application error
    Traceback (most recent call last):
      File "/Applications/sage/local/lib/python2.7/site-packages/Twisted-12.3.0-py2.7-macosx-10.6-x86_64.egg/twisted/python/threadpool.py", line 195, in _worker
        o = self.q.get()
      File "/Applications/sage/local/lib/python2.7/site-packages/Twisted-12.3.0-py2.7-macosx-10.6-x86_64.egg/twisted/python/context.py", line 118, in callWithContext
        return self.currentContext().callWithContext(ctx, func, *args, **kw)
      File "/Applications/sage/local/lib/python2.7/site-packages/Twisted-12.3.0-py2.7-macosx-10.6-x86_64.egg/twisted/python/context.py", line 83, in callWithContext
        self.contexts.pop()
      File "/Applications/sage/local/lib/python2.7/site-packages/Twisted-12.3.0-py2.7-macosx-10.6-x86_64.egg/twisted/web/wsgi.py", line 340, in run
        self.started = True
    --- <exception caught here> ---
      File "/Applications/sage/local/lib/python2.7/site-packages/Twisted-12.3.0-py2.7-macosx-10.6-x86_64.egg/twisted/web/wsgi.py", line 315, in run
        appIterator = self.application(self.environ, self.startResponse)
      File "/Applications/sage/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 "/Applications/sage/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 "/Applications/sage/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 "/Applications/sage/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 "/Applications/sage ...