It seems a lot of people have had this problem and there doesn't seem to be many absolute fixes for it.
I have a multisite set up running locally (through MAMP pro), and i've uploaded to my development server to test upon.
My first problem was that none of my permalinks works - this was because I had to set SUBDOMAIN_INSTALL to false in the wp-config. I had already logged in to wp-admin before I set this to true. I have 4 sites and they are running like
siteone.domain.com (obvious why i needed SUBDOMAIN_INSTALL to be set to true!)
Okay - so now it's set to true, i try to log in to wp-admin from another machine and it screws up big time. It just redirects to the re-auth=1 admin login page, time after time. Not a cookie or cache problem, tried on multiple machines and browsers to no joy.
If i set the SUBDOMAIN_INSTALL back to false, I can log in again, without a problem. This works, but I cannot present my client with the fact they need to change a config file every time they need to get into the admin panel to update the website, bound to be trouble
Can anyone help me with this? I've tried different wp-config setups, different .htaccess setups, removing wp-admin/install.php and more, none seem to fix this problem. Whilst logged in with the subdomain_install set to false, I also went and flushed the permalinks for each site hoping this would fix the problem. No joy.
Any help appreciated, this is doing my nut in, literally.