IOError

[E 20:32:59.036 NotebookApp] Error while saving file: /Untitled.ipynb disk I/O error 
    Traceback (most recent call last):
      File "/scratch/gaa/local/src/anaconda/lib/python2.7/site-packages/IPython/html/services/contents/filemanager.py", line 383, in save
        self.check_and_sign(nb, path) 
      File "/scratch/gaa/local/src/anaconda/lib/python2.7/site-packages/IPython/html/services/contents/manager.py", line 428, in check_and_sign
        self.notary.sign(nb)
      File "/scratch/gaa/local/src/anaconda/lib/python2.7/site-packages/IPython/nbformat/sign.py", line 248, in sign
        self.store_signature(signature, nb)
      File "/scratch/gaa/local/src/anaconda/lib/python2.7/site-packages/IPython/nbformat/sign.py", line 251, in store_signature
        if self.db is None: 
      File "/scratch/gaa/local/src/anaconda/lib/python2.7/site-packages/IPython/utils/traitlets.py", line 412, in __get__
        value = method()
      File "/scratch/gaa/local/src/anaconda/lib/python2.7/site-packages/IPython/nbformat/sign.py", line 129, in _db_default
        self.init_db(db)
      File "/scratch/gaa/local/src/anaconda/lib/python2.7/site-packages/IPython/nbformat/sign.py", line 141, in init_db
        )""") 
    OperationalError: disk I/O error 
[W 20:32:59.038 NotebookApp] Unexpected error while saving file: /Untitled.ipynb disk I/O error 
[E 20:32:59.038 NotebookApp] {
      "Content-Length": "19",.
      "Accept-Language": "en-US,en;q=0.5",.
      "Accept-Encoding": "gzip, deflate",.
      "Cache-Control": "no-cache",.
      "Connection": "keep-alive",.
      "Accept": "application/json, text/javascript, */*; q=0.01",.
      "User-Agent": "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:36.0) Gecko/20100101 Firefox/36.0",.
      "Host": "",.
      "X-Requested-With": "XMLHttpRequest",.
      "Pragma": "no-cache",.
      "Cookie": "__utma=170659492.1716016652.1397056628.1397056628.1397056628.1; _ga=GA1.2.1716016652.1397056628; username--9999=\"2|1:0|10:1428429582|30:username--es-9999|48:ODJlYjgyMmQtMDQwNy00MWY5LWI0NTItMGU3NmNhYTZmNWNh|72b21758fcd382eee1b579b393b92d2a64b81e5c8f1a4a187db30154b09f9d28\"",.
      "Referer": "https:///tree/",.
      "Content-Type": "application/x-www-form-urlencoded; charset=UTF-8"
    }
[E 20:32:59.038 NotebookApp] 500 POST /api/contents/ (XXX.XXX.XX.XX) 8.28ms referer=https://:9999/tree/