Add the accounts 'NT Authority\Network Service' and 'NT Authority\System' as valid users and grant the sysadmin role to 'NT ...

Add the accounts 'NT Authority
etwork Service' and 'NT Authority\System' as valid users and grant the sysadmin role to 'NT Authority\System' account on the default instance of Microsoft SQL Server by following the instructions at http://msdn.microsoft.com/en-us/library/aa337562.aspx.