Redmine

I had the repository feature working in my Redmine (using the latest version,
on Ubuntu Linux, running Apache).
The repo setting was pointing right at the repository on the same
machine as Redmine, so the path looked like this:
/prj/repos/r1
Then I added a second repository, I'm using Mercurial by the way:
/prj/repos/r2
So I thought I would tell Redmine to use the path:
/prj/repos
I did that by logging in as admin and deleting the current repo setting.
Since then I have not been able to display any repository. Not even
by going back to the original setting of /prj/repos/r1

All I get when I click on the Repository tab is this, in red:
The entry or revision was not found in the repository.

How do I fix this?

Thanks,
Greg Strockbine