Featured images no longer appear after wordpress update

The issue we faced is when the current version of WordPress was updated to the latest one i.e. 3.4.1.

Problem area –> I am having featured images set for many posts in my WordPress, and it is a multisite network. When i update my WordPress to 3.4.1 80% of my featured images are not appearing on my website. The problem is in all the sites except my home site. The images are there in my media library, but when i open in my post the featured image is not available there. It is working fine when i re-upload images to my post.

I have Tried Deactivating all the plugins and activating them again, but that didn’t work.

I am not using any plugins for the featured image.