I have a similar problem. I create a linked server, as:

exec sp_addlinkedserver 'ADSITest', 'My Active DirectoryTest', 'ADSDSOObject',

'adsdatasource'

go

exec sp_addlinkedsrvlogin 'ADSITest', false, 'username',

'username', 'password'

go

select * from openquery(ADSI, 'SELECT *...