Merge to Pano in LR gives "Unknown Errors Occurred" (PS works fine?)

I am unable to merge a series of 9 photographs into a panorama in LR - I keep getting an error message "Unknown errors occurred".

However, using the same 9 images, I have no problem in Photoshop.  My preference would be to 'stay' in LR..

All software is currently up-to-date: LR CC 2015.9; Camera Raw 9.9; PS 2017.01.  The images are unaltered (except for ALL having a clarity adjustment of approx 20 in LR).  I can obviously continue to use PS, but can anybody advise me as to what the problem could be here..