DOCBOOK: EpcEdit and SGML DocBook

[GCS <gcs@agentsinside.com>]

Hello,

 I am trying to create an SGML file, with the v4.1 DocBook DTD. The editor is
EpcEdit. But I get:
cannot generate system indentifier for public text "-//OASIS//ENTITIES DocBoon Notations V4.1//EN"
reference entity "dbnotn" for which is no system indentifier could be generated
cannot generate system indentifier for public text "-//OASIS//ENTITIES DocBoon Character Entities V4.1//EN"
reference entity "dbcent" for which is no system indentifier could be generated
...

Can someone please help me out what I am doing wrong?
Thanks,
Laszlo