I’m getting the same thing. I had previously done an install with WP3.0b1 and it worked fine. I just tried doing exactly the same install procedure (from careful notes) but on a different account using WP3.0b2 but when I create a second test blog under the WP MU Super User I get 404’s. Racking my brains against the screen here…
I’ve been Googling this issue a lot and it would seem that the solution is going to be somehow related to rewrite and/or permissions. I’ve checked mine already but try the following:
– Make sure your .htaccess file is in the root directory and has 755 permissions. Might be obvious to you, but make sure the .htaccess file didn’t get saved in .txt mode when the appropriate rewrite code was added. (i.e., “save as – file type ALL, not txt, even if you name it correctly simply as “.htacess”. If it’s your own server, this should be sufficient for activating rewrite, but if it’s a 3rd party server, make sure they don’t have to do something from their end too to activate a la Apache rewrite.
– Make sure your respective blog directories are set for 755 too.