Error when using format mask to create download link in report

Question

I'm following these directions to create a download link in a report region.
http://docs.oracle.com/cd/E23903_01/doc/doc.41/e21674/advnc_blob.htm#HTMDB25905
######### Table Structure...
desc document_library
Name Null Type
DOC_ID NOT NULL VARCHAR2(40)
DATE_ADDED NOT NULL DATE
FILE_CONTENT BLOB()
FILE_NAME VARCHAR2(100)
MIME_TYPE VARCHAR2(100)
DOC_NUMBER NUMBER
###### Report Region...
select a.*, dbms_lob.getlength(file_content) length
from document_library a
###### Download Link Column...
Date Format: DOWNLOAD:DOCUMENT_LIBRARY:FILE_CONTENT:DOC_NUMBER::MIME_TYPE:FILE_NAME:::attachment:Download
####### Results...
report error:
ORA-06502: PL/SQL: numeric or value error: character to number conversion error
The report region displays no rows (even though there is one row in the table), no links, and even more strange, it show the value of APP_USER where it would normally display the results.

Answer 1

Josh,
Your end result on page 58 and the instructions in that document link don't seem to correlate. Regardless, I:
1) Copied page 58 to page 158 in your application.
2) Removed the BLOB format mask from your report link.
3) Changed your query to:
select "ROWID",
"DOC_ID",
"DATE_ADDED",
"USER_ID",
dbms_lob.getlength("FILE_CONTENT") "FILE_CONTENT",
"FILE_NAME",
"MIME_TYPE",
"DOC_NUMBER"
from "#OWNER#"."DOCUMENT_LIBRARY"
4) Specified the BLOB format mask for the FILE_CONTENT column.
Seems to work just fine now (on page 158, that is).
Joel