There are several issues with the approach you took:

TensorFlow Object Detection API models need to be preprocessed before you can convert them to TFLite. You need to follow the steps listed here 4 before the conversion. @Sayak_Paul also wrote a blog post 2 about it.
TFLite only supports SSD models, so you won’t be able to convert the Faster RCNN model to TFLite even if you follow the steps above.

So if you want to do object detection with TFLite, my recommendation would be using EfficientDet-Lite via Model Maker, or use the MobileDets models in TF Object Detection API if you want to customize the model architecture.

  
      

      TensorFlow
  

  
    

Object Detection with TensorFlow Lite Model Maker