I first verified that my 1.6.6 and 1.7 versions were operating as expected. (These installations anyway.) And my upgrade of the 1.6.6. version to 1.9.4.2 seems to be fine. However using the same procedure for the 1.7 version didn't work. This is what I did in both cases.
- Logged out of admin (not sure that matters)
- Extracted the base 1.9.4.2 system over top of the existing systems
- logged in to admin and clicked continue until it was done.
However the 1.7 upgrade won't load. I just get a "loading" message in the browser. But I can access the admin page and if I go to global settings and change the site to maintenance mode then when accessing the page it loads as expected with the maintenance message. Then returning to the admin page and clearing the maintenance check box reverts back to the same never loading situation.
The other difference of these two systems is that the original 1.6.6 version was accessed via a domain and the 1.7 was a subdomain but as mentioned they both worked fine as 1.6.6 and 1.7 now only the 1.6.6 upgraded version works.
Stumped.