Python Keras Tensorflow Embedding Layer Indices[i,j] = k is not in [0,max_features]

Question

I am trying to do Author Identification, my train_vecs_w2v.shape = (15663, 400). y_train.shape = (15663,3) which has 3 label one hot encoded. Now the problem is I am having an error in the Embedding layer. Indices[0,X] = -1 is not in [0, 15663). How to solve this? Is it my code or Keras/Tensorflow?

print('Building Model')
n=19579
max_features = 15663
max_length = 400
EMBEDDING_DIM = 100
model7 = Sequential()

model7.add(Embedding(len(train_vecs_w2v), EMBEDDING_DIM, input_length=max_length, dtype='float32', trainable=True, weights=None, embeddings_initializer='uniform', embeddings_regularizer=None, activity_regularizer=None, embeddings_constraint=None))
print(model7.output_shape)
model7.add(Convolution1D(filters =128, kernel_size = 3, strides=1, activation='relu', use_bias=False, border_mode='same')) 
print(model7.output_shape)
model7.add(MaxPooling1D(pool_size = 3))
print(model7.output_shape)
model7.add(Convolution1D(filters = 64, kernel_size = 5, strides=1, activation='relu', border_mode='same'))
print(model7.output_shape)
model7.add(MaxPooling1D(pool_size = 5))
print(model7.output_shape)
model7.add(Flatten()) # model.output_shape == (None, 64*input_shape of convolution layer)
print(model7.output_shape)
model7.add(Dense(output_dim = 64, activation='relu')) # input_shape = (batch_size, input_dim)
print(model7.output_shape)
model7.add(Dense(output_dim = 32, activation='relu'))
print(model7.output_shape)
model7.add(Dense(output_dim = 3, activation='softmax'))

model7.compile(optimizer='adam',
              loss='categorical_crossentropy',
              metrics=['categorical_accuracy'])

model7.fit(train_vecs_w2v, y_train_vec, epochs=50, batch_size=32, verbose=2)

The error I am getting

InvalidArgumentError (see above for traceback): indices[0,1] = -1 is not in [0, 15663)
     [[Node: embedding_1/Gather = Gather[Tindices=DT_INT32, Tparams=DT_FLOAT, validate_indices=true, _device="/job:localhost/replica:0/task:0/device:CPU:0"](embedding_1/embeddings/read, embedding_1/Cast)]]

Answer 1

I think the problem here is with the word vectors count.
It should be

len(train_vecs_w2v) + 1