Q: Failed to verify the preflight file. It is not signed by Apple.

Thanks. Changing the Certificate preferences in Keychain worked for me as well.

Marking the certificates to 'Best attempt' worked for me.

Bingo! Worked for me too.

Set keychain access > preferences > certificates > off for both protocol and revocation list.

This worked. Thanks.

Nice work. This also worked for me.

I too had the same problem and changing the keychain preference worked for me.  What I find frustrating is that we have to go search for fixes to problems like this.  Apple's quality assurance process seems to have failed!

lexayles explanation worked for me.  For some reason my imovie and iphoto were reporting the same issues as everyone else apps.  So far so good and as I understand things after this I can turn back the keychain access settings and I wont have the same issues for the above mentioned apps...???... Will see I guess. Wont bother stating the disappointment shared with many users about the decline of apple products and there bugs post release but I will say I agree. How the importance of one man can be such a difference in a huge company I just dont understand.

Changing certificates preferences didn't work for me.  However, I had recently installed Splashtop Streamer.  When I exited that program which was running in the background, everything updated just fine.

The keychaine solution worked for me too.  Thank you.  Now if Apple can just figure out why, so no one else wastes 30 minutes at a Genius Bar with a tech indicating that he thinks my HD is crashing. 

Just had another update to do.  Again, same problem.  Please ignore my previous post.  Changing the Keychain Access certificate preferences to "Off" worked this time.  Once I changed them I had to close the preference window to make it work. 

What amazes me is that 5596 people have viewed this thread so far, yet no reply or fix from Apple!

Michael A. N.,

Thank you for figuring this out and sharing with the rest of us!

@Eiresurg, that's because this is a primarily a user forum. You should make issues you have with OS X known to Apple by doing a bug report. Just choose "bug report…" from Feedback Type in the form.

In OS X 10.9 Mavericks all I had to do to solve this issue was making sure Certificate settings were set at "Best Attempt" instead of "Require If…". I also deleted expired and non-trusted certificates (Including one non-expired but untrusted Thawte) before this, but that wasn't sufficient.

Thank you! This is the best solution here. I do not want to change my certificate preferences and water down my security—"Require if certificate indicates" is the correct setting. I hadn't seen this problem in quite a while, but it popped up again today and this resolved it.