HDR Photomerge

I've seen this discussion previously but nothing to fix the issue... Perhaps I've missed it but I could really use the help.

Ive been attempting to do a Photomerge using "exposure bracketed" photos from my D750. It has been successful on 2 attempts however it has failed on at least 10. one selecting the photos (imported) and clicking Photomerge/HDR the software appears to be working for about 5 seconds and then says that it is unable to merge my selected files... select cancel and review. I've followed steps from multiple forums/tutorial videos to no avail. The software has been uninstalled and reinstalled LR 6 (6.9)

PC hardware exceeds minimum requirements of software.