Sequences already exists error


when this changeSet executed , the implicit sequence was generated on the table message_sent column bssentmsgid.

After generate changeLog performed ,all tables,indexes,constraints and sequences will be generarted in a single xml file.afte that if i execute lb_install.bat on empty schema,sequence already exists errot coming. i am trying to drop the implicit sequence ,but it’s giving error like can’t drop implicit sequences,drop table is recommended.if i drop the table i lost it’s content. to resolve this problem?
i am using postgresql data base.

please help anyone,thanks in Advance…