Werkzeug Internal Server Error

traceback.txt

Traceback (most recent call last):
  File "/home/guyja/python/.virtenv/dmtco/lib/python2.7/site-packages/flask/app.py", line 1836, in __call__
    return self.wsgi_app(environ, start_response)
  File "/home/guyja/python/.virtenv/dmtco/lib/python2.7/site-packages/pony/utils.py", line 45, in pony_wrapper
    return caller(func, *args, **kwargs)
  File "/home/guyja/python/.virtenv/dmtco/lib/python2.7/site-packages/pony/orm/core.py", line 331, in new_func
    try: return func(*args, **kwargs)
  File "/home/guyja/python/.virtenv/dmtco/lib/python2.7/site-packages/flask/app.py", line 1820, in wsgi_app
    response = self.make_response(self.handle_exception(e))
  File "/home/guyja/python/.virtenv/dmtco/lib/python2.7/site-packages/flask/app.py", line 1403, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/home/guyja/python/.virtenv/dmtco/lib/python2.7/site-packages/flask/app.py", line 1817, in wsgi_app
    response = self.full_dispatch_request()
  File "/home/guyja/python/.virtenv/dmtco/lib/python2.7/site-packages/flask/app.py", line 1477, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/home/guyja/python/.virtenv/dmtco/lib/python2.7/site-packages/flask/app.py", line 1381, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/home/guyja/python/.virtenv/dmtco/lib/python2.7/site-packages/flask/app.py", line 1475, in full_dispatch_request
    rv = self.dispatch_request()
  File "/home/guyja/python/.virtenv/dmtco/lib/python2.7/site-packages/flask/app.py", line 1461, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/home/guyja/python/dmtco/views.py", line 261, in purge_transaction
    purge_transactions()
  File "/home/guyja/python/dmtco/models.py", line 45, in purge_transactions
    db.drop_table('MaterialTransaction', with_all_data=True)
  File "<string>", line 2, in drop_table
    
  File "/home/guyja/python/.virtenv/dmtco/lib/python2.7/site-packages/pony/utils.py", line 96, in cut_traceback
    return func(*args, **kwargs)
  File "<string>", line 2, in drop_table
    
  File "/home/guyja/python/.virtenv/dmtco/lib/python2.7/site-packages/pony/orm/core.py", line 325, in new_func
    throw(TransactionError, '%s cannot be called inside of db_session' % func)
  File "/home/guyja/python/.virtenv/dmtco/lib/python2.7/site-packages/pony/utils.py", line 123, in throw
    raise exc
TransactionError: drop_table() cannot be called inside of db_session