It looks like an improvement made to the validator depends on a newer version of SGML::Parser::OpenSP then when the guide was written.
I assume you grabbed the "single zip file" containing all the modules you needed, which appears to be maintained on a non-w3c host (presumably by the module author).
I suggest upgrading to the latest version of SGML::Parser::OpenSP through PPM, and then reporting the bug through the feedback channel mentioned at the bottom of the page you linked to.
David Dorward
2010-04-21 09:11:59