Object detection with Pascal VOC 2007 with fastai v1

HI, I wanted to know has anyone tried Object detection with Pascal VOC 2007 dataset in fastai v1? I am facing some trouble in bounding box classifier that @jeremy did in last year’s course. I am not able to do tfm_y for proper bounding boxes. Here is an error that I am getting-

My dataframe from which I am creating ImageList looks like this-

The bbl1,…bbl4 represent the four coordinates of the bounding box for the respective image under fn column.

Any way to get around this problem? Can I represent the labels in any better way for it to work or am I missing something in my transformation function to make it work?

there is an example here with Retinanet https://github.com/fastai/course-v3/blob/master/nbs/dl2/pascal.ipynb