Keras bug NasNetlarge no top
What is your keras version? Two things you could try are:


Update your keras to latest version
If the above does not work, open the nasnet.py file in keras, and change this part of the code:

elif default_size == 331:  # large version
    if include_top:
        weight_path = NASNET_LARGE_WEIGHT_PATH
        model_name = 'nasnet_large.h5'
    else:
        weight_path = NASNET_LARGE_WEIGHT_PATH_NO_TOP
        model_name = 'nasnet_large_no_top.h5'

    weights_file = get_file(model_name, weight_path,
                            cache_subdir='models')
    model.load_weights(weights_file)


to this:

elif default_size == 331:  # large version
    if include_top:
        weight_path = NASNET_LARGE_WEIGHT_PATH
        model_name = 'nasnet_large.h5'
    else:
        weight_path = NASNET_LARGE_WEIGHT_PATH_NO_TOP
        model_name = 'nasnet_large_no_top.h5'

    weights_file = get_file(model_name, weight_path,
                            cache_subdir='models')
    model.load_weights(weights_file, by_name = True)