SQL Developer Data Modeler

I have a relational model in DM and select menu Export / DDL File.
I leave the selection Oracle Database 11g and click Generate.
In the new dialog I leave everything as is (all tables and other items selected) and click OK.
The result is just some comments:

-- Generated by Oracle SQL Developer Data Modeler 3.0.0.665
-- at: 2011-02-24 18:45:45 CET
-- site: Oracle Database 11g
-- type: Oracle Database 11g


-- Oracle SQL Developer Data Modeler Summary Report:
--
-- CREATE TABLE 0
-- CREATE INDEX 0
-- ALTER TABLE 0
-- more here, I deleted for brevity
-- DROP TABLESPACE 0
-- DROP DATABASE 0
--
-- ERRORS 0
-- WARNINGS 0


With some other model, it works.
Any idea what to look for?

I also tried Oracle SQL Developer 3.0 Early Adopter 4 (3.0.03.97), but it is the same there too (just comments are created).


I also tried to export just one table, but the result is same, just the above comments.

Regards,
David