This week's book giveaway is in the Cloud/Virtualization forum. We're giving away four copies of Cloud Application Architecture Patterns: Designing, Building, and Modernizing for the Cloud and have Kyle Brown, Bobby Woolf and Joseph Yodor on-line! See this thread for details.
The XML looks valid. The DTD doesn't specify a value attribute for the property element (hence the error), however no property element in Angus's xml file has a value attribute. Which leads me to think that perhaps there is another invalid hibernate.cfg.xml file kicking around in your deployment maybe?
(In addition to the online tool you suggest you can just use IE to validate XML against schemas).