Q: Why does it want me to re-download itunes to redeem a digital version of Jurassic Park 3?

Hi, chidpanda.  

Thank you for visiting Apple Support Communities.  

I understand that you are unable to redeem a Digital Copy as you need to redownload iTunes.  Can you tell me what version of iTunes you are currently using?  This can be found via the Help menu and About iTunes.  Also, what is the exact error message that you are receiving?  In the interim, lets try completely removing iTunes, all of its components and reinstall.  These steps will not delete any of your media.  Once this is done, test downloading the Digital Copy.  

Remove and reinstall iTunes and related software components for Windows

If you run into any issues during the uninstall, please take a look at the information in the article below.  

If you can't install or update iTunes for Windows

Cheers