I downloaded it on my mac and unzipped it and everything appears to be in order. Which operating system are you using?. I would appreciate if you could provide more information that I could use(your operating system and your untar utility). In case you are you windows, try untarring it with 7zip rather than the windows default unzip tool. 

This issue also occurs if the file download is not complete.

Hope that helps,
Regards,
sharad