Can not process blob file in interactive report

I created an interactive report that includes qry'ing a blob file [which is a scanned document], and i want to give the user the option to download or view the scanned document[attachment to invoice, e.g.]

the query is:

select distinct

I.invoice_id,

I.invoice_num,

vendor_name,

invoice_amount,

inv_status,

invoice_received_date,

invoice_date,

sys.dbms_lob.getlength(file_data) download_image,

sys.dbms_lob.getlength(file_data) view_image

from

XXNEO_AP_INVOICES_MV@APEX_EBS_DBLINK I,

XXNEO_AP_INVC_ATTACH_APEX_MV A

WHERE 

I.INVOICE_ID = NVL(:P103_INVOICE_ID, I.INVOICE_ID)