Whenever this has been reported in the past, the cause has always been that the user has downloaded the wrong set of files.
It is easy to accidentally download 2010 instead of 2007 or Expert instead of Essential.
Make sure you select the correct title and then download again.
If you are having problems downloading or installing the sample files read this help topic which includes a step-by-step guide to downloading and using the sample files:
If you still have any questions, click here to post a new topic and provide full details of the problem.