Problem building documentation

[INFO] Processing input file: dhis2_implementation_guide.xml
Error
  Failure reading
/home/knutst/dhis/dhis2-docbook-docs/src/docbkx/en/dhis2_implementation_guide.xml:
/home/knutst/dhis/dhis2-docbook-docs/src/docbkx/en/docbookV4.5/docbookx.dtd
(No such file or directory)
[INFO] ------------------------------------------------------------------------
[ERROR] BUILD ERROR
[INFO] ------------------------------------------------------------------------
[INFO] Failed to transform dhis2_implementation_guide.xml.

Embedded error: Failure reading
/home/knutst/dhis/dhis2-docbook-docs/src/docbkx/en/dhis2_implementation_guide.xml
/home/knutst/dhis/dhis2-docbook-docs/src/docbkx/en/docbookV4.5/docbookx.dtd
(No such file or directory)

···

--
Cheers,
Knut Staring