I tried to do this this afternoon, and as before, I found something really annoying happening. It created all sorts of error messages after the initial upload of files.

Here’s the solution…

1. Open “/mu/wp-blog-header.php”
2. Locate line 9: if ( !file_exists( dirname(__FILE__) . '/wp-config.php')
&& !file_exists( dirname( dirname(__FILE__) ) . '/wp-config.php')) {
3. Edit this line to be: if ( !file_exists( dirname(__FILE__) . '/wp-config.php') ) {

Hope this is useful sometime, I know it will be to me!