OK. I ran the Wave Profiler and that seems t have done it.
SO. sforzando can load and play the sfz and the files associated. But Rupture and Dimentia Pro still fail. I have moved the piano fold across to c:\programme files and into C:\Program Files\Cakewalk\Dimension Pro\Multisamples(for some reason all my stuff has been installed in C:\Program Files x86\Cakewalk\Dimension Pro\Multisamples, but that seems to work OK), with the wav files still in its subdirectory.
AHah! this is interesting. Here is the _full_ error message in the log file
File c:\program files\cakewalk\dimension pro\multisamples\kawaiuprightpiano-20170128\samples not found or couldn't be loaded.
So it's looking for a file named samples, not a wav file in that folder?