I've had this same issue. I'm upgrading my solution manually, as it's a slightly different file structure and have followed the instructions
I tried the emergency admin reset, but it resulted in the following server error:
Server Error in '/' Application.
Invalid column name 'UserIsEditor'.
Invalid column name 'UserIsGlobalAdministrator'.
Invalid column name 'UserSiteManagerDisabled'.
I'm aware these columns have been removed as part of the Kentico 10 upgrade, which suggests that there's legacy code/dlls still in my solution.
I've been through the dlls being referenced (they're all v10) and currently double checking the code files, but would be grateful if anyone has any ideas as-to what I might have missed.