GAE - Deployment Error: "AttributeError: can't set attribute"
This also happens if your default_error value overlaps with your static_dirs in app.yaml.
When I try to deploy my app I get the following error:

Starting update of app: flyingbat123, version: 0-1
Getting current resource limits.
Password for avigmati: Traceback (most recent call last):
  File "C:\Program Files (x86)\Google\google_appengine\appcfg.py", line 125, in 
    run_file(__file__, globals())
  File "C:\Program Files (x86)\Google\google_appengine\appcfg.py", line 121, in run_file
    execfile(script_path, globals_)
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\appcfg.py", line 4062, in 
    main(sys.argv)
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\appcfg.py", line 4053, in main
    result = AppCfgApp(argv).Run()
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\appcfg.py", line 2543, in Run
    self.action(self)
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\appcfg.py", line 3810, in __call__
    return method()
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\appcfg.py", line 3006, in Update
    self.UpdateVersion(rpcserver, self.basepath, appyaml)
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\appcfg.py", line 2995, in UpdateVersion
    self.options.max_size)
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\appcfg.py", line 2122, in DoUpload
    resource_limits = GetResourceLimits(self.rpcserver, self.config)
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\appcfg.py", line 355, in GetResourceLimits
    resource_limits.update(GetRemoteResourceLimits(rpcserver, config))
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\appcfg.py", line 326, in GetRemoteResourceLimits
    version=config.version)
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\appengine_rpc.py", line 379, in Send
    self._Authenticate()
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\appengine_rpc.py", line 437, in _Authenticate
    super(HttpRpcServer, self)._Authenticate()
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\appengine_rpc.py", line 281, in _Authenticate
    auth_token = self._GetAuthToken(credentials[0], credentials[1])
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\appengine_rpc.py", line 233, in _GetAuthToken
    e.headers, response_dict)
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\appengine_rpc.py", line 94, in __init__
    self.reason = args["Error"]
AttributeError: can't set attribute
2012-04-25 19:30:15 (Process exited with code 1)

The following is my app.yaml:

application: flyingbat123
version: 0-1
runtime: python
api_version: 1
threadsafe: no

It seems like an authentication error, but I'm entering a valid email and password. 
What am I doing wrong?