<type 'exceptions.TypeError'>: 'str' object is not callable
Traceback (most recent call last):
  File "/base/data/home/apps/d-crawl/beta.347907494409487783/admin.py", line 28, in <module>
    from google.appengine.ext.db import djangoforms
  File "/base/python_runtime/python_lib/versions/1/google/appengine/ext/db/djangoforms.py", line 472, in <module>
    class ModelChoiceField(forms.Field):
  File "/base/python_runtime/python_lib/versions/1/google/appengine/ext/db/djangoforms.py", line 475, in ModelChoiceField
    'invalid_choice': _(u'Please select a valid choice. '
<type 'exceptions.TypeError'>: 'str' object is not callable