You might try the web.config file at this site:
https://lauragentry.com/blog/2010/07/30/how-to-create-a-wordpress-3-0-multisite-network-on-a-windows-server-using-sub-directories/
I just migrated to a Windows server and couldn’t see all my sites and starting receiving the same error. I tried her file and can see all sites and no error.
