Notebook does not want to open

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Hi there, I'm using Sage 5.11 on Mac OS 10.6. Until about 1 year ago, the notebook used to open but now when opening Sage.app it does not (safari says it can't open localhost:8080). I can use the terminal and from there call notebook(), but then I get the following error:

Please wait while the Sage Notebook server starts...
Traceback (most recent call last):
  File "/Applications/Sage-5.11-OSX-64bit-10.6.app/Contents/Resources/sage/local/bin/sage-notebook", line 34, in <module>
    notebook()
  File "/Applications/Sage-5.11-OSX-64bit-10.6.app/Contents/Resources/sage/devel/sagenb/sagenb/notebook/notebook_object.py", line 223, in __call__
    return self.notebook(*args, **kwds)
  File "/Applications/Sage-5.11-OSX-64bit-10.6.app/Contents/Resources/sage/devel/sagenb/sagenb/notebook/run_notebook.py", line 528, in notebook_run
    nb = notebook.load_notebook(directory)
  File "/Applications/Sage-5.11-OSX-64bit-10.6.app/Contents/Resources/sage/devel/sagenb/sagenb/notebook/notebook.py", line 1797, in load_notebook
    nb = Notebook(dir)
  File "/Applications/Sage-5.11-OSX-64bit-10.6.app/Contents/Resources/sage/devel/sagenb/sagenb/notebook/notebook.py", line 150, in __init__
    S.load_users(self._user_manager)
  File "/Applications/Sage-5.11-OSX-64bit-10.6.app/Contents/Resources/sage/devel/sagenb/sagenb/storage/filesystem_storage.py", line 267, in load_users
    for user in self._basic_to_users(self._load('users.pickle')).itervalues():
  File "/Applications/Sage-5.11-OSX-64bit-10.6.app/Contents/Resources/sage/devel/sagenb/sagenb/storage/filesystem_storage.py", line 167, in _load
    result = cPickle.load(f)
EOFError

Has someone got an idea what to do? Thanks so much.