CCX gradebook exception related to https://odl.zendesk.com/agent/tickets/3501

ccx-gradebook-exception

Jul 25 19:55:21 ip-10-4-10-203 [service_variant=lms][django.request][env:prod-edge-edxapp] ERROR [ip-10-4-10-203 31177] [base.py:256] - Internal Server Error: /courses/ccx-v1:MITx+7.00x+2T2015+ccx@343/ccx_gradebook
Traceback (most recent call last):
File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/core/handlers/base.py", line 132, in get_response
response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/newrelic-2.64.0.48/newrelic/hooks/framework_django.py", line 503, in wrapper
return wrapped(*args, **kwargs)
File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/views/decorators/cache.py", line 43, in _cache_controlled
response = viewfunc(request, *args, **kw)
File "/edx/app/edxapp/edx-platform/lms/djangoapps/ccx/views.py", line 103, in wrapper
return view(request, course, ccx)
File "/edx/app/edxapp/edx-platform/lms/djangoapps/ccx/views.py", line 502, in ccx_gradebook
student_info, page = get_grade_book_page(request, course, course_key=ccx_key)
File "/edx/app/edxapp/edx-platform/lms/djangoapps/instructor/views/gradebook_api.py", line 96, in get_grade_book_page
for student in enrolled_students
File "/edx/app/edxapp/edx-platform/lms/djangoapps/instructor/offline_gradecalc.py", line 92, in student_grades
return grades.grade(student, course, keep_raw_scores=keep_raw_scores)
File "/edx/app/edxapp/edx-platform/lms/djangoapps/courseware/grades.py", line 272, in grade
grade_summary = _grade(student, course, keep_raw_scores, course_structure)
File "/edx/app/edxapp/edx-platform/lms/djangoapps/courseware/grades.py", line 302, in _grade
course_structure = get_course_blocks(student, course.location)
File "/edx/app/edxapp/edx-platform/lms/djangoapps/course_blocks/api.py", line 66, in get_course_blocks
starting_block_usage_key,
File "/edx/app/edxapp/edx-platform/openedx/core/lib/block_structure/manager.py", line 66, in get_transformed
unicode(self.root_block_usage_key),
UsageKeyNotInBlockStructure: ("The requested usage_key '{0}' is not found in the block_structure with root '{1}'", u'ccx-block-v1:MITx+7.00x+2T2015+ccx@343+type@course+block@course', u'ccx-block-v1:MITx+7.00x+2T2015+ccx@343+type@course+block@course')