Cannot assign the admin role
The admin role definition contains a scoped role.
You could go to the "contains role" related list and click edit to remove the contains role record. This might cause another error "If that role contains is removed, no active users or admins will be able to access the application anymore" due to PRB1331826. The workaround for this issue was to de-activate the ScopedAdministration script include and then delete the contains role record. Then re-activate the script include.