I am writing the code for deep learning, but an error occurred and I cannot proceed, and I do not know the details of the error, so please let me know.

from keras.applications.vgg16import VGG16
from keras.models import Sequential
from keras.models import model_from_json
from keras.models import Model
from keras.layers import Input, Activities, merge, Dense, Flatten, Dropout
from tensorflow.keras.optimizers import Adam

input_tensor=Input(shape=(224,224,3))
base_model=VGG16(weights='imagenet', input_tensor=input_tensor, include_top=False)

# afterthought

top_model=Sequential()
top_model.add(Flatten(input_shape=base_model.output_shape[1:]))
top_model.add(Dense(n_classes, activation='softmax'))

# connection

model=Model(inputs=base_model.input, outputs=top_model(base_model.output))

# the unlearned class

for layer in model.layer [:15]:
  layer.trainable=False

print('#layer=',len(model.layer))

model.compile(loss='categorical_crossentropy', optimizer='adam', metrics=['accuracy'])
model.summary()