bulk load mystery

hello ...

I've got sql2005 running under domain account.
When I try to run this query from query analyzer remotely on server:
SELECT * FROM OPENROWSET(BULK N'\\host\obr1.jpg', SINGLE_BLOB) as aaa
i get error message:
Cannot bulk load because the file "\\host\obr1.jpg" could not be
opened. Operating system error code 5(error not found).

But when I run same query under same user but loged locally on server
everything works fine.

When I try to check permissions file with runnig over runas command
and sqlserver running account (on sql server or on remote client)
everything looks ok I can read file.

Users are member of bulkadmin role.

what the problem ?

thanks for any hint.