4.2 blob download format mask not working

Question

I am using Apex 4.2
I have been working through the book Beginning Oracle Application Express 4. In chapter 6 the a blob is added to a report.
I have pasted the code example into the report definition (albeit with my own page numbers) :
SELECT
   "TICKET_DETAILS"."TICKET_DETAILS_ID" "TICKET_DETAILS_ID",
   "TICKET_DETAILS"."TICKET_ID" "TICKET_ID",
   "TICKET_DETAILS"."DETAILS" "DETAILS",
   "TICKET_DETAILS"."CREATED_ON" "CREATED_ON",
   "TICKET_DETAILS"."CREATED_BY" "CREATED_BY",
   dbms_lob.getlength("ATTACHMENT") ATTACHMENT
FROM
   "TICKET_DETAILS"
WHERE (("TICKET_DETAILS"."TICKET_ID" = :P5_TICKET_ID))
I go to the report attributes and click on the attachment column.  I enter the suggested format mask
DOWNLOAD:TICKET_DETAILS:ATTACHMENT:TICKET_DETAILS_ID::MIME_TYPE:FILE_NAME:::inline:Download.
When I press apply I keep getting :
1 error has occurred
"" not found. (Go to error)
I have confirmed that the query runs and that P5_TICKET_ID does exist on page 5.
Not understanding what this meant I tracked down this page
17.10 About BLOB Support in Forms and Reports
and the section "Providing a Download Link" seems to confirm that the above format mask is correct.
Any pointers would be greatly appreciated.

Answer 1

I've also done the exercises in the book and it worked for me.
Your format mask is correct. But before pressing submit you also have to enter the blob column attributes:
*Format Mask (Value Required):                   DOWNLOAD
*Blob Table (Value Required):                       TICKET_DETAILS
*Blob Column (Value Required):                   ATTACHMENT
*Primary Key Column 1 (Value Required):     TICKET_DETAILS_ID
Primary Key Column 2:
Mimetype Column:                                      MIME_TYPE
Filename Column:                                       FILE_NAME
Last Updated Column
Character Set Column:
Content Disposition:                                    ATTACHMENT
Download Text:                                           Download
Maybe you forgot that?