Hi, I've seen the error and here is my solution (I promise it will work for you guys, too)
Go to your phpmyadmin. Select the name of the database which your wordpress mu is using. Go to Search.
At the: Word(s) or value(s) to search for (wildcard: "%") type: dashboard_blog
Then on the Inside table(s): you have to scroll down and select wp_sitemeta to be inserted in the Search. OK, just click Go.
You will have the search resources above like this:
Search results for "dashboard_blog" at least one of the words:
2 match(es) inside table wp_sitemeta | Browse | Delete
Click Browse and you will see 2 table. Edit the table name dashboard_blog.
Whatever you see the meta_value is. I don't remember exactly (may be ERROR and something) but you don't need to worry. Just delete all and type 1. Yes, just type the word "1" in the box ONLY.
Finally, click Go. And log in to you WP. See the result.
It works for me and I hope that it works for you, too.
Have a nice day!