I decided to upgrade from 1.2.3 to 1.2.5a tonight. I get an error which I traced to the wpmu-functions.php file. I uploaded my old one to fix the error, but obviously I need to fix this :)
The error seems to be related to the wp-plugins.
Fatal error: Cannot redeclare switcher_scripts() (previously declared in /home/site/public_html/blogs/wp-includes/wpmu-functions.php:1742) in /home/site/public_html/blogs/wp-content/mu-plugins/dashboardswitcher.php on line 5
I deleted the dashboardswitcher.php file and then it displayed the same error, but with the next wp-plugin file loaded (delete-blog.php).
TIA :)