Multiple File Access

Hello, We are writing an application in access which accepts an order number.
We use the order number to read a non-access db file to retrieve the customer
number - this works fine. We would like to use the customer number to read an
additional file to retrieve the customer name but are unable to make this work.
Can anyone help please?
Additional info: In the access program we are using dlookup to retrieve the customer number from
the non access data base. This is working and the accss field is being populated correctly. We
would like to use this field to read an additional file to retrieve additional data. We seem unable to
string two dlookups together. Is this possible? regards
Private sub order_afterupdate()
accno = dlookup("customer_code", "dbo_firstfile", "order_number= forms! [rsd]![order]")
End sub
This works well, but when we include an additional statement;
name = dlookup ("customer_name", "arrcustomers", "customer_code = forms! [rsd] ! [accno]")
end sub
no data is returned.