Thank you Yann for investigating this for me - I really appreciate it.
I am using the 64bit version of FastPictureViewer from http://www.fastpictureviewer.com/downloads/
I believe the download version works for a few weeks without needing to be purchased.
Just to give you more information, I can make use of Panotour and Autopano Tour if I drag the files into the app instead of trying to browse to them in the usual manner. Saving can be hazardous if the destination folder has jpegs in it - the app will crash, sometimes not immediately but after several seconds , as if it were taking time to find the jpegs before giving the error.
My impression is that the error is only produced when using an open/save window which happens to have jpegs in the folder.
If you need any further information, let me know.