Are you sure this is the correct chapter in the book, because when I looked this up, all I managed to find was 'Electronic forms' and that page was just an introduction to it.
However, by the looks of your code (whether or not it was just a posting error), it's because you have missed a '<' bracket.
<object data="data:application/x-silverlight," type="application/x-silverlight" width="400" height="400">
Also, don't forget to close this tag, and make sure it is embedded correctly into your code. Where is this piece of code located? It's hard to tell without enough code as it may be a different part that is stopping this from working correctly.