Thank you for the reply. I had the same error message before and it was resolved when I removed a casting of a header value from unicode to str. Now in this case I can't see where that happens or what causes the error. The full trace I'm experiencing now is
File "/media/Lexar/montao/google/appengine/runtime/wsgi.py", line 129, in _StartResponse raise InvalidResponseError('headers must be str') InvalidResponseError: headers must be str INFO 2011-12-31 04:55:36,484 recording.py:372] Saved; key: __appstats__:034800, part: 137 bytes, full: 27325 bytes, overhead: 0.001 + 0.008; link: http://localhost:8080/_ah/stats/details?time=1325307334890 ERROR 2011-12-31 04:55:36,484 wsgi.py:186] Traceback (most recent call last): File "/media/Lexar/montao/google/appengine/runtime/wsgi.py", line 175, in Handle for chunk in result: File "/media/Lexar/montao/google/appengine/ext/appstats/recording.py", line 926, in appstats_wsgi_wrapper result = app(environ, appstats_start_response) File "/media/Lexar/montao/lib/webapp2/webapp2.py", line 1524, in __call__ return self._internal_error(e)(environ, start_response) File "/media/Lexar/montao/lib/webapp2/webapp2.py", line 1522, in __call__ return response(environ, start_response) File "/media/Lexar/montao/lib/webob/webob/__init__.py", line 2000, in __call__ start_response(self.status, self.headerlist) File "/media/Lexar/montao/google/appengine/ext/appstats/recording.py", line 923, in appstats_start_response return start_response(status, headers, exc_info) File "/media/Lexar/montao/google/appengine/runtime/wsgi.py", line 129, in _StartResponse raise InvalidResponseError('headers must be str') InvalidResponseError: headers must be str -- http://mail.python.org/mailman/listinfo/python-list