Cobol/400 and DDS

Hi!

I'm actually trying to get familiar with Cobol programming on a AS/400
machine. I've got a DDS Screen description, the ususal kind of file
executed with EXFMT within RPG. I'd like to call this screen format
from Cobol now. I declared it that way:

In FILE-CONTROL:
SELECT SCREEN-FILE ASSIGN TO WORKSTATION-SCREEN ORGANIZATION IS
TRANSACTION.

In FILE-SECTION:
FD  SCREEN-FILE LABEL RECORDS ARE STANDARD.
01  SCREEN-REC.
COPY DDS-ALL-FORMATS OF BUKTODSP.

In PROCEDURE DIVISION:
OPEN I-O SCREEN-FILE.
WRITE SCREEN-REC FORMAT IS "D1KONTO".
READ SCREEN-FILE RECORD.
CLOSE SCREEN-FILE.

Well, I know there is no error checking done in this sample program.
The AS/400 responds with a LBE7207 exception during the OPEN
statement. So it seems the WORKSTATION-SCREEN cannot be opened. But
why? The COPY is expanded to the single records in the DDS file, so
this file is found. What can be the reason for the open failure of the
SCREEN-FILE?

Sorry if this question is too stupid, I've been used to program in the
VMS environment.

Luke