Does anyone know how to correct this or what does this mean?

Odoo Server Error

Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/openerp/http.py", line 643, in _handle_exception
    return super(JsonRequest, self)._handle_exception(exception)
  File "/usr/lib/python2.7/site-packages/openerp/http.py", line 680, in dispatch
    result = self._call_function(**self.params)
  File "/usr/lib/python2.7/site-packages/openerp/http.py", line 316, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/usr/lib/python2.7/site-packages/openerp/service/model.py", line 118, in wrapper
    return f(dbname, *args, **kwargs)
  File "/usr/lib/python2.7/site-packages/openerp/http.py", line 309, in checked_call
    result = self.endpoint(*a, **kw)
  File "/usr/lib/python2.7/site-packages/openerp/http.py", line 959, in __call__
    return self.method(*args, **kw)
  File "/usr/lib/python2.7/site-packages/openerp/http.py", line 509, in response_wrap
    response = f(*args, **kw)
  File "/usr/lib/python2.7/site-packages/openerp/addons/web/controllers/main.py", line 892, in call_kw
    return self._call_kw(model, method, args, kwargs)
  File "/usr/lib/python2.7/site-packages/openerp/addons/web/controllers/main.py", line 884, in _call_kw
    return getattr(request.registry.get(model), method)(request.cr, request.uid, *args, **kwargs)
  File "/usr/lib/python2.7/site-packages/openerp/api.py", line 250, in wrapper
    return old_api(self, *args, **kwargs)
  File "/usr/lib/python2.7/site-packages/openerp/api.py", line 381, in old_api
    result = method(recs, *args, **kwargs)
  File "/usr/lib/python2.7/site-packages/openerp/models.py", line 6035, in onchange
    record._onchange_eval(name, field_onchange[name], result)
  File "/usr/lib/python2.7/site-packages/openerp/models.py", line 5939, in _onchange_eval
    method_res = getattr(self._model, method)(*args, context=self._context)
  File "/usr/lib/python2.7/site-packages/openerp/api.py", line 250, in wrapper
    return old_api(self, *args, **kwargs)
  File "/usr/lib/python2.7/site-packages/openerp/addons/website/models/res_config.py", line 34, in on_change_website_id
    website_data = self.pool.get('website').read(cr, uid, [website_id], [], context=context)[0]
  File "/usr/lib/python2.7/site-packages/openerp/api.py", line 250, in wrapper
    return old_api(self, *args, **kwargs)
  File "/usr/lib/python2.7/site-packages/openerp/models.py", line 3175, in read
    result = BaseModel.read(records, fields, load=load)
  File "/usr/lib/python2.7/site-packages/openerp/api.py", line 248, in wrapper
    return new_api(self, *args, **kwargs)
  File "/usr/lib/python2.7/site-packages/openerp/models.py", line 3210, in read
    self._read_from_database(stored, inherited)
  File "/usr/lib/python2.7/site-packages/openerp/api.py", line 248, in wrapper
    return new_api(self, *args, **kwargs)
  File "/usr/lib/python2.7/site-packages/openerp/models.py", line 3401, in _read_from_database
    res2 = self._columns[f].get(cr, self._model, ids, f, user, context=context, values=result)
  File "/usr/lib/python2.7/site-packages/openerp/osv/fields.py", line 1497, in get
    result = self._fnct(obj, cr, uid, ids, name, self._arg, context)
  File "/usr/lib/python2.7/site-packages/openerp/addons/website_sale/models/sale_order.py", line 142, in _get_pricelist_id
    pricelist = self.get_current_pricelist(cr, uid, context=context)
  File "/usr/lib/python2.7/site-packages/openerp/api.py", line 250, in wrapper
    return old_api(self, *args, **kwargs)
  File "/usr/lib/python2.7/site-packages/openerp/addons/website_sale/models/sale_order.py", line 225, in get_current_pricelist
    available_pricelists = self.get_pricelist_available(cr, uid, context=context)
  File "/usr/lib/python2.7/site-packages/openerp/api.py", line 250, in wrapper
    return old_api(self, *args, **kwargs)
  File "/usr/lib/python2.7/site-packages/openerp/addons/website_sale/models/sale_order.py", line 203, in get_pricelist_available
    request.website.user_id.sudo().partner_id.property_product_pricelist.id,
AttributeError: 'NoneType' object has no attribute 'user_id'