I am using a Leica M Monochrom (first version, not the new 246). I have tried to stitch together 4-8 images (raw DNG files) several times and I cannot get to the preview stage. It says "generating Preview", and then abruptly quits, with the error msg "Unknown errors occurred."
I know the Pano function in CC is working because I have created several Panos from Nikon D800E raw NEF files. I otherwise do not have difficulty with Leica DNG files from this camera, I just cannot do panoramas.