Q: Failed to verify preflight file ... App Store broken after Mavericks upgrade

What worked for me was changing the certificate preferences in Keychain Access (open Keychain Access app and then go to preferences).

I just changed both of the first two options to 'Best Attempt', they were originaly at 'Require if certificate indicates'.

Hope this Helps

Very helpful solution - it worked perfectly for me and now I can upgrade previously purchased apps including Pages and Numbers.

Thnx a bunch, worked for me too...

Thank you so much for the fix! 

Be Patient, I kept getting the same message, I "Repaired disk permissions and safe startup" as recommended on Support Chat. Eventually received a message from iCloud stating: Updates are available to download. Everything went smoothly updating all my Apple App's and Upgrading Pixelmator to V3... 

you should indicate that p1991atric answered your question, as this correction worked perfectly and immedicately.

How?

What worked for me was changing the certificate preferences in Keychain Access (open Keychain Access app and then go to preferences).

I just changed both of the first two options to 'Best Attempt', they were originaly at 'Require if certificate indicates

If you are going to copy and paste my solution, please do it on another discussion page/question. I don't mind if you share what I posted around the internet, just not on the same discussion.

I had the same issue, this resolution worked great for me.  Thank you.

Thanks for all your replies, I had something deeply wrong with my ability to read my HDD.. Had my first appointment with the "Genius Bar" at Norwich store since purchase of my Mac and had a most interesting and successful time..

Now this problem is solved if you install updates after installing Mavericks.  Go to App Store | Updates | Install all updates.

This is better than the workaround of disabling some certificate security features.

This did it for me as well. Dunno if there's a security risk in doing it, but it got me past the hurdle, thanx!!

Thank you p1991atric