ROI selection for film dosimetry

Hello, I am new to the Slicer Film Dosimetry module. I am running through the steps and using the example data provided. However, I am stuck at the region selection stage for calibration. I could not add ROI after clicking on the Add Region. Attached is the image of the calibration window. Any help would be great, thank you.

This extension is not maintained anymore, so it is probable that your issue is due to the API changes since then, see

Maybe you can try the film dosimetry extension with an older version of Slicer, such as 4.10.

Or you can try to fix the extension for the latest version if you feel motivated. I can give pointers if you decide to go for it.