Downloading a file via a procedure works in one app but not another

Question

Obviously I've overlooked something. I have this procedure (following). It works in one application that has been running for a couple years. It is called from Column Link with this value #OWNER#.DOWNLOAD_ATTACHED_FILES?p_file=#DOWNLOAD_LINK#
I'm now making a new application and want the same facility but this same procedure gives me a page not found error even though the error page URL looks like: .../apex/GMCTRL.DOWNLOAD_ATTACHED_FILES?p_file=42 which seems to me that it should work correctly. (the row with the value 42 does exist in the DB)
Is there a setting/flag/thing that I have to set to make this work in my new application that I've overlooked? (both are APEX 3.1.1 and oracle 11g)
create or replace PROCEDURE "DOWNLOAD_ATTACHED_FILES" (p_file in number) AS
v_mime VARCHAR2(48);
v_length NUMBER;
v_file_name VARCHAR2(2000);
Lob_loc BLOB;
BEGIN
SELECT MIME_TYPE, RPT_DOCUMENT_BLOB_IMG, RPT_DOCUMENT_FILE_NAME_TX, DBMS_LOB.GETLENGTH(RPT_DOCUMENT_BLOB_IMG)
INTO v_mime, lob_loc,v_file_name,v_length
FROM RPT_DOCUMENT_BLOB
WHERE RPT_DOCUMENT_BLOB_ID = p_file;
owa_util.mime_header( nvl(v_mime,'application/octet'), FALSE );
htp.p('Content-length: ' || v_length);
htp.p('Content-Disposition: attachment; filename="'||substr(v_file_name,instr(v_file_name,'/')+1)|| '"');
owa_util.http_header_close;
wpg_docload.download_file( Lob_loc );
end download_attached_files;

Answer 1

Hello:
Ensure that
GMCTRL.DOWNLOAD_ATTACHED_FILES is executable by oracle account used by APEX to connect to the database (apex_public_user or anonymous)
GMCTRL.DOWNLOAD_ATTACHED_FILES is included into 'WWV_FLOW_EPG_INCLUDE_MOD_LOCAL' as an authorized procedure. See Re: link can't find a stored procedure
Varad