After installing ZMM on my Windows 2008 R2 server, the web/management site doesn't let me login and says "Login Failed"

At the end of the Web component installation, when it asked for an email address and password, I entered (for example) and a password.

On the login page I've tried:

Password: <my password>
Domain: <blank>

Username: admin
Password: <my password>

And other variations, but none of them work.

I've also reinstalled it from scratch 3 times to make sure I entered the correct information without typos. Updating to the latest version doesn't fix it either. Also worth noting that the updater accepted the email and password I entered during installation, so I know I'm not typing them wrong.