The model of faster rcnn training problem, it fails

Hi there,
I met with some issues when using the example program from gluoncv to fine-tune the fasterrcnn with the model of faster_rcnn_fpn_resnet101_v1d_coco in gluoncv model zoo.

the codes are here,and the errors are also included: https://gist.github.com/jewelcai/08167cc7eaa98f929a9cc4846692e221