training stop unexpectedly

Hi, I prepared the data for training insightface as described in the [guide](https://github.com/Talgin/preparing_data) of @Talgin . However, when the training start, this following error occured:

> **$ CUDA_VISIBLE_DEVICES='' python -u train.py --network r100 --loss arcface --dataset ktnv**
use cpu
prefix ./models/r100-arcface-ktnv/model
image_size [112, 112]
num_classes 37
Called with argument: Namespace(batch_size=128, ckpt=3, ctx_num=1, dataset='ktnv', frequent=20, image_channel=3, kvstore='device', loss='arcface', lr=0.1, lr_steps='100000,160000,220000', models_root='./models', mom=0.9, network='r100', per_batch_size=128, pretrained='', pretrained_epoch=1, rescale_threshold=0, verbose=2000, wd=0.0005) {'bn_mom': 0.9, 'workspace': 256, 'emb_size': 512, 'ckpt_embedding': True, 'net_se': 0, 'net_act': 'prelu', 'net_unit': 3, 'net_input': 1, 'net_blocks': [1, 4, 6, 2], 'net_output': 'E', 'net_multiplier': 1.0, 'val_targets': ['lfw'], 'ce_loss': True, 'fc7_lr_mult': 1.0, 'fc7_wd_mult': 1.0, 'fc7_no_bias': False, 'max_steps': 0, 'data_rand_mirror': True, 'data_cutoff': False, 'data_color': 0, 'data_images_filter': 0, 'count_flops': True, 'memonger': False, 'loss_name': 'margin_softmax', 'loss_s': 64.0, 'loss_m1': 1.0, 'loss_m2': 0.5, 'loss_m3': 0.0, 'net_name': 'fresnet', 'num_layers': 100, 'dataset': 'ktnv', 'dataset_path': '../datasets/ktnv', 'num_classes': 37, 'image_shape': [112, 112, 3], 'loss': 'arcface', 'network': 'r100', 'num_workers': 1, 'batch_size': 128, 'per_batch_size': 128}
0 1 E 3 prelu False
Network FLOPs: 24.2G
INFO:root:loading recordio ../datasets/ktnv/train.rec...
header0 label [38. 42.]
id2range 4
37
rand_mirror True
loading bin 0
(456, 3, 112, 112)
ver lfw
lr_steps [100000, 160000, 220000]
call reset()
/home/extreme45nm/anaconda3/lib/python3.7/site-packages/mxnet/module/base_module.py:504: UserWarning: Optimizer created manually outside Module but rescale_grad is not normalized to 1.0/batch_size/num_workers (1.0 vs. 0.0078125). Is this intended?
optimizer_params=optimizer_params)
Traceback (most recent call last):
File "train.py", line 379, in
main()
File "train.py", line 376, in main
train_net(args)
File "train.py", line 370, in train_net
epoch_end_callback = epoch_cb )
File "/home/extreme45nm/anaconda3/lib/python3.7/site-packages/mxnet/module/base_module.py", line 520, in fit
next_data_batch = next(data_iter)
File "/home/extreme45nm/anaconda3/lib/python3.7/site-packages/mxnet/io/io.py", line 230, in next
return self.next()
File "/home/extreme45nm/anaconda3/lib/python3.7/site-packages/mxnet/io/io.py", line 476, in next
raise StopIteration
StopIteration

I am stuck at this point, please give me some hint to solve this.