Error "ora-01031: insufficient privilige" when connecting as SYSDBA to database in 'Upgrade' mode
This is an Oracle limitation. When a database is in 'Upgrade' mode it is only possible to connect on the server itself with the sql*plus. If connecting remotely via sql*plus or Toad, the above error will result.
The database must be mounted and in 'Open' mode in order to connect remotely via Toad or sql*plus.