ora-06512 in dbms_lob.read

Hi All,

This is part of procedure that sends email from our database.

WHILE(offset < v_request_length) LOOP

        dbms_lob.read(j_request, amount, offset, buffer);

        r_req:=utl_raw.cast_to_raw(buffer);

  utl_http.write_raw (req,r_req);

  offset := offset + amount;

  END LOOP;            

The procedure sends a json request using utl_http.

We have weird case,

when "j_request" parameter is: Req: {"to":["AAA@BBB.COM"],"subject":"p","text":"ג","attachments":[]}  (value of "subject" field has English characters and "text" field has Hebrew characters or opposite) then email is sent without any errors,

but when "j_request" parameter is: Req: {"to":["