Talked with PaulVH on problems administering users and connections in Contribute. He confirmed similar problems involving pathnames and urls. We also did some testing with file permissions on the server and with email addresses for the user of the key and those didn't seem to have any effect.

I installed Contribute on an Intel Mac laptop and the program installed properly (as opposed to the PowerPC G5 where it does not seem to install properly).
Then I tried to create a connection to the French site. When I provided this for the URL to the site:
http://web.uvic.ca/french
at the start of the wizard, then later when it came to specifying the path on the server, everything went well
If I specified
http://web.uvic.ca/french/web_pages/index.php (which is the actual URL of the page - the index.htm page at the root is a redirect to web_pages/index.php)
then later when I specified the path, I got the "could not confirm" error message.

So, it seems that when I provide the exact information on the URL and path of the home page, Contribute is deriving paths from that information which are wrong, whereas if I provide the url and path to the root of the site and let Contribute work out the redirects itself, it gets that right.