Evaluating a tracking result from MOTS

I am trying to see evaluation results using MOTS dataset and tools. I am following this link –https://github.com/VisualComputingInstitute/mots_tools . I am in the Evaluating a tracking result section. When tried to execute the command
python mots_eval/eval.py tracking_results gt_folder seqmap I am facing an error. Here is the error message I am getting.

Here seqmap file is exactly copied from fulltrain.seqmap , gt_folder has Annotations in txt format and tracking_results is copied from TrackR-CNN tracking result. I have tried with Annotations in png format but getting the same error. Please let me know what I am doing wrong