Multisite: Network migration okay; can't login?

I just completed a migration of a multisite network from one domain to another (using BackupBuddy as directed in the webinar video here: https://ithemes.com/codex/page/BackupBuddy_Multisite).

The migration itself seems to have gone okay — the files are there, I can see the main network site, etc.

However, when I go to mydomain.com/wp-admin (and it goes to https://mydomain.com/wp-login.php?redirect_to=http%3A%2F%2Fmydomain.com%2Fwp-admin%2F&reauth=1) and enter username/password, it just empties out the username and password and loops back through to that same screen.

Any thoughts?

Thanks!