My installation is saying that, too, but rewrite module is installed.  Dashboard also says Web server - undefined.  None of my URLs work.  I've even tried turning off permalinks, and it ignores the settings.  /page/login /page/anything gives me a 404 page not found, and URL structure doesn't change with permalink set to off.  Don't want to log out of the studio for fear I can't get back in.

Is there supposed to be some kind of rewrite rules put into the .htaccess file? Mine is pretty much blank except for php.ini directives.  If the installer is supposed to put some in, it didn't do it.

(Running 10.0.0.B1 since there doesn't seem to be a download link for version 9 available)