WordPress MU

Well after a long comedy of errors, I got a localhost running offline under Windows, and I got MU installed - even though I couldn't do much.
I'm trying to mirror my live site so I can test things before an upgrade, so I've restored a backup to my localhost install. Now I get "No WPMU site defined on this host."

Any ideas? I've just about run out of brain power. It all looks so simple typed out like that, but it's taken me so long so far (2+ hours today alone) because of stupid user errors (yes, mine) and it's incredibly frustrating.

Don't use localhost! Use localhost.localdomain or make up a domain and hostnames.

And it'll still run locally, locked tight behind firewalls?
(just checking before I dent the desktop again)

yup.

I really, really hate to bug you... where would I put this change? During the (re)install process? Or can I just edit a file somewhere? (or maybe 2 somewheres)

Since you're on Windows, create a file called "hosts" in your windows directory. Make sure it's not hosts.txt or anything else.
Put the following line in there:
127.0.0.1 testdomain.com

Save and restart your browser. If your install of Apache has only one virtual host then open http://testdomain.com/ in your browser and you should see something delivered by Apache. It will probably be the "No WPMU at this site" message.
You will have to reinstall or if you really like making trouble for yourself, changing all urls in wp_site, wp_blogs, wp_*_options that reference localhost to testdomain.com ..

If you're looking to mirror your production environment for testing purposes, I would *highly* recommend setting up a virtual machine using VMware. I do this on my laptop and then create a hosts file which points my domain to the virtual machine. It's a great way to test because you can use the snapshot feature to quickly rollback if you break things. If you can't afford VMware workstation, you can use the free VMware Server or Microsoft's Virtual Server.

Donncha - hubby would say I must like making trouble for myself since I seem to be in it so often... Anyway, got it working after he got home as our setup is not default.

The hosts file had to go in c:\windows\system32\drivers\etc\hosts in case anyone else has this issue. We also wound up using desktop.local as a domain.

Still testing it thouygh. I could make a test blog, but as it needs email activiation and I don't have that set up, I'm moving on to testing a backup (probably tomorrow).

Thanks for the suggestion amanzi. It was mostly due to unfamiliarity with our specific setup. We've got enough developer tools on here as it is and we're trying to move away from getting more MicroSuck tools. :)