ValueError: Unknown layer: Merge

[LLDavid]

I got this error when I test on an image:

File "predict_mass.py", line 39, in
main()
File "predict_mass.py", line 35, in main
output = predict_mass(filename,dims)
File "predict_mass.py", line 17, in predict_mass
output = shape_aware_model.predict((im,dims))
File "/home/.../PyCode/Downloaded/image2mass/model_wrapper.py", line 99, in predict
self.thickenss_model = keras.models.load_model('thickness_model.h5')
File "/usr/local/lib/python3.5/dist-packages/keras/engine/saving.py", line 261, in load_model
model = model_from_config(model_config, custom_objects=custom_objects)
File "/usr/local/lib/python3.5/dist-packages/keras/engine/saving.py", line 335, in model_from_config
return deserialize(config, custom_objects=custom_objects)
File "/usr/local/lib/python3.5/dist-packages/keras/layers/init.py", line 55, in deserialize
printable_module_name='layer')
File "/usr/local/lib/python3.5/dist-packages/keras/utils/generic_utils.py", line 145, in deserialize_keras_object
list(custom_objects.items())))
File "/usr/local/lib/python3.5/dist-packages/keras/engine/network.py", line 1036, in from_config
process_layer(layer_data)
File "/usr/local/lib/python3.5/dist-packages/keras/engine/network.py", line 1022, in process_layer
custom_objects=custom_objects)
File "/usr/local/lib/python3.5/dist-packages/keras/layers/init.py", line 55, in deserialize
printable_module_name='layer')
File "/usr/local/lib/python3.5/dist-packages/keras/utils/generic_utils.py", line 145, in deserialize_keras_object
list(custom_objects.items())))
File "/usr/local/lib/python3.5/dist-packages/keras/engine/network.py", line 1036, in from_config
process_layer(layer_data)
File "/usr/local/lib/python3.5/dist-packages/keras/engine/network.py", line 1022, in process_layer
custom_objects=custom_objects)
File "/usr/local/lib/python3.5/dist-packages/keras/layers/init.py", line 55, in deserialize
printable_module_name='layer')
File "/usr/local/lib/python3.5/dist-packages/keras/utils/generic_utils.py", line 138, in deserialize_keras_object
': ' + class_name)
ValueError: Unknown layer: Merge

Seems like a Keras version problem. Anyone knows how to solve it?
Thanks