"Oracle Error: -22275/ORA-22275:invalid LOB locator specified"/dbms_lob.freetemporary

/* Function pck_raw.if_read_long_raw() */

function if_read_long_raw(ps_tableName in varchar2, ps_rawColumn in varchar2, ps_pkColumn in varchar2, pde_pkValue in number, pb_blobData out nocopy blob, pde_ht_id out number)
return number is

de_id number default 0;
de_status number default 1;
de_return number default 1;

begin
de_id := pck_raw.if_create_empty_blob();
pde_ht_id := de_id;

pck_message_proz.ipr_debug_message('id geholt. id: '||de_id);

/* 1 */
de_status := pck_raw.if_read(ps_tableName,ps_rawColumn, ps_pkColumn, pde_pkValue, de_id);

/* 2 */
select htb_blob into pb_blobData from ht_blob where htb_instanz = de_id;

return de_return;
end if_read_long_raw;

/* 1 */
/* Reads a Long raw from the specified Table an Column and stores the Data into table
"ht_blob" with the primary key de_id */

/* 2 */
/* Selects the written Blob from this table "ht_blob" into the overgiven blob */


/* This is a piece of my package */
/* this part creates a temporary blob, calls the function below and frees the temp. blob */

-------------------------------

bl_file blob;

dbms_lob.createtemporary(bl_file,true);

-- Read a long-Raw from DB into bl_file
de_status := pck_raw.if_read_long_raw('druckdokumentenzst','drdz_dokument', 'drdz_instanz', de_key_instanz, bl_file, de_ht_id);

/* 3 */
dbms_lob.freetemporary(bl_file);

--------------------------------

Now my problem is, that when i call dbms_lob.freetemporary(bl_file) /* 3 */ a
"Oracle Error: -22275/ORA-22275: invalid LOB locator specified" occours.

Does anyone know why??

Thanks for helping..

Flo..