I downloaded Joe Workman’s PagesSafe stack to trial and installed ok. The stack comes with some sample files. I clicked a sample file to open whereupon it was opened with RW6. When I tried to open my site which is in RW7 (upgrade), nothing. When I searched application, no sign of RW7. I tried using Time Machine to restore to the last back-up but to no avail. So I had to download RW7 again and install from scratch. All issues resolved.
To try and find out what happened, I right clicked the sample file to see which application it would open with and found it had been set presumably by JW to RW6. When I changed open with to RW7 everything was ok again.
In future, rather than assume a stack sample file is up to speed, I shall check which version of RW it is pre-set to open with and change it if need be.