sometimes it is easier to do it in sql
if your name is the asset tag use this
UPdate dbo.Inv_Asset_Tag
SEt [Barcode] = dbo.inv_asset_tag.[asset tag]
from dbo.inv_asset_tag
left outer join altiris.dbo.Inv_Aex_AC_identification
ON dbo.inv_asset_tag.[_Resourceguid]= altiris.dbo.Inv_Aex_AC_identification.[_resourceGuid]
Where dbo.Inv_Asset_Tag.[barcode] IS NULL
AND dbo.inv_asset_tag.[asset tag] LIKE 'IS%'