Q: Made I movie ...trying to share it using I DVD but 7.2.1 update require

Why is there no iDVD on my new Mac? How do I get it and how do I install it?

https://discussions.apple.com/docs/DOC-3673

To burn a DVD with iDVD from the latest version of iMovie, you have to export the movie using the Export button and select 480p as the size. Open iDVD and start a new project, then drag that exported movie file into the iDVD menu window, avoiding any drop zones you see.

Do you currently have any version of  iDVD 7 installed?  If so then you can use this updater: iDVD 7.1.2. Otherwise read what Klaus1 has posted and linked to.