Assert(graph_def.node[0].op == 'Placeholder') IndexError: list index out of range

I trained a custom model and i want to run it in opencv dnn and i tired and got this error please help
thanks
E:\mask_rcnn_inception_v2_coco_2018_01_28\opencv\sources\samples\dnn>tf_text_graph_mask_rcnn.py --input E:\mask_rcnn_inception_v2_coco_2018_01_28\mask_rcnn_resnet101_atrous_coco_2018_01_28\mask_rcnn_landing.pb --config E:\mask_rcnn_inception_v2_coco_2018_01_28\mask_rcnn_resnet101_atrous_coco_2018_01_28\pipeline.config --output E:/output.pbtxt
Number of classes: 90
Scales: [0.25, 0.5, 1.0, 2.0]
Aspect ratios: [0.5, 1.0, 2.0]
Width stride: 16.000000
Height stride: 16.000000
Features stride: 8.000000
Traceback (most recent call last):
File “E:\mask_rcnn_inception_v2_coco_2018_01_28\opencv\sources\samples\dnn\tf_text_graph_mask_rcnn.py”, line 86, in
assert(graph_def.node[0].op == ‘Placeholder’)
IndexError: list index out of range