Error AssertionError

[isaquer]

File "/jet/var/python/lib/python3.6/threading.py", line 916, in _bootstrap_inner
self.run()
File "/jet/var/python/lib/python3.6/threading.py", line 864, in run
self._target(*self._args, **self._kwargs)
File "/jet/prs/workspace/pi/train.py", line 125, in processThread
model = PluginLoader.get_model(trainer)(get_folder(self.arguments.model_dir))
File "/jet/prs/workspace/pi/PluginLoader.py", line 13, in get_model
return PluginLoader.import("Model", "Model{0}".format(name))
File "/jet/prs/workspace/pi/PluginLoader.py", line 22, in _import
module = import(name, globals(), locals(), [], 0)
File "/jet/prs/workspace/pi/Model_Original.py", line 3, in
from keras.models import Model as KerasModel
File "/jet/var/python/lib/python3.6/site-packages/keras/init.py", line 3, in
from . import utils
File "/jet/var/python/lib/python3.6/site-packages/keras/utils/init.py", line 6, in
from . import conv_utils
File "/jet/var/python/lib/python3.6/site-packages/keras/utils/conv_utils.py", line 3, in
from .. import backend as K
File "/jet/var/python/lib/python3.6/site-packages/keras/backend/init.py", line 71, in
assert _backend in {'theano', 'tensorflow', 'cntk'}
AssertionError