Hi All
Nope to all the suggestions above – the resolution was far simpler than all of you are looking at, and I’m very surprised Andrea didn’t think of it (but then I didn’t either and I have a long-standing bug report in trac about it).
In WPMU 2.9.2 and earlier, the final screen of install is about 3 screen heights tall – at the top it gives the master admin username and password followed by a “login now” button. A LONG way down that page it says to delete or rename the /wp-admin/install.php file BEFORE trying to login.
WP 3.0 does not have that warning anywhere in the install screens, nor the readme, nor anywhere in the codex. On a hunch, I tried doing exactly that – BINGO – got straight in.
When I get a minute, I’ll file another bug report in trac about this.
Hope it helps you all
Gaz