I have a similar problem!
I was running happily a 3.0.1 version (multisite), but since the Post Voting settings panel did not show I decided to take the risk and update my network. I did a backup of the Data Base and the site)
As usual, upgrading made my site crash :slight_frown: trying to get back the site from the backups dis not work. Is there is any issue that make it not possible (maybe because the file is 2.77GB size)
With my hosting company I made available the site again. They confirmed there was an issue with the ALL-IN-SEO plugin and the site became visible again.
But now I can´t reach the network admin. Pressing the network admin at the top right hand which should lead to this address: http://www.severus.es/wp-admin/network/ I get the following message after a while:
The page isn't redirecting properly
Firefox has detected that the server is redirecting the request for this address in a way that will never complete.
* This problem can sometimes be caused by disabling or refusing to accept
My multisite has not superadmin since I am like a normal user. Other thing is that the site is not able to find and show some of the images. You could see it here: http://www.severus.es
Since I can´t edit or manage or upload themes, plugins or edit files; I have requested my hosting company to deinstall all the plugins of the network. I am waiting if that help.
Any idea how to solve it?
I saw a similar issue in this thread here: https://premium.wpmudev.org/forums/topic/update-network
Upgrading Wordpress should be forbidden!