django - "'django_mongodb_engine' isn't an available database backend" when pushing to Heroku -

i have django app ran on heroku , uses mongodb engine. of sudden, can not push anymore. not seem recognize django_mongodb_engine module anymore. reverted changes version last ran, it's still same. suspect version conflict or so, can not figure out how fix it.

this error i'm getting:

traceback (most recent call last):   file "manage.py", line 10, in <module>     execute_from_command_line(sys.argv)   file "/app/.heroku/python/lib/python2.7/site-packages/django/core/management/__init__.py", line 429, in execute_from_command_line     utility.execute()   file "/app/.heroku/python/lib/python2.7/site-packages/django/core/management/__init__.py", line 379, in execute     self.fetch_command(subcommand).run_from_argv(self.argv)   file "/app/.heroku/python/lib/python2.7/site-packages/django/core/management/base.py", line 191, in run_from_argv     self.execute(*args, **options.__dict__)   file "/app/.heroku/python/lib/python2.7/site-packages/django/core/management/base.py", line 220, in execute     output = self.handle(*args, **options)   file "/app/.heroku/python/lib/python2.7/site-packages/django/core/management/base.py", line 351, in handle     return self.handle_noargs(**options)   file "/app/.heroku/python/lib/python2.7/site-packages/django/core/management/commands/shell.py", line 46, in handle_noargs     django.db.models.loading import get_models   file "/app/.heroku/python/lib/python2.7/site-packages/django/db/__init__.py", line 78, in <module>     connection = connections[default_db_alias]   file "/app/.heroku/python/lib/python2.7/site-packages/django/db/utils.py", line 93, in __getitem__     backend = load_backend(db['engine'])   file "/app/.heroku/python/lib/python2.7/site-packages/django/db/utils.py", line 51, in load_backend     raise improperlyconfigured(error_msg) django.core.exceptions.improperlyconfigured: 'django_mongodb_engine' isn't available database backend.  try using django.db.backends.xxx, xxx 1 of:     'dummy', 'mysql', 'oracle', 'postgresql', 'postgresql_psycopg2', 'sqlite3' error was: no module named utils 

and these important parts requirements.txt:

hg+https://bitbucket.org/wkornewald/django-nonrel git+https://github.com/django-nonrel/mongodb-engine hg+https://bitbucket.org/wkornewald/djangotoolbox  pymongo==2.2.1 pytz==2012d 

i'm confused because reverted changes. code same configuration ran (and still on production server), pushing not work.

thanks simon

of course, when asked on figure out answer :-)

i don't know why exactly, defining exact revision want check out solved problem.

so requirements.txt looks this:

-e hg+http://bitbucket.org/wkornewald/django-nonrel@be48c152abc6b15e45155e2bbcfd69c665ccb536#egg=django-dev -e git+https://github.com/django-nonrel/mongodb-engine@52257b5d90dcfaa564e708264a9cfe591d301fe6#egg=django_mongodb_engine-dev -e hg+https://bitbucket.org/wkornewald/djangotoolbox@a8cdf61ba9c0cdc7cbbbd37d693e9a222d9a8e5f#egg=djangotoolbox-dev  pymongo==2.2.1 pytz==2012d