One Class:

The final output .txt file start with 0 and corresponding x,y,w and h when you ran convert.py. Please check the all .txt file, if it’s has start with 0. Beacuase 0 means class 1.

Yolo V2 Conf:

Set the filters = 30 in line num 237 and classes = 1 in line num 244 if you are using yolov2.cfg.
If you are using tiny-yolo.cfg please refer my blog.

You can start training….