Did you check to see if Network Service has permissions in the new instance?
select left(name,25) name, type, type_desc
from sys.server_principals AS log
WHERE (log.type in ('U', 'G', 'S', 'R'))
AND Name LIKE 'NT%'
order by 3,1
Argue for your limitations, and sure enough they're yours (Richard Bach, Illusions)