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

Worked for me as well.

OK, I found something that worked - will any of you seeing this problem try it out?

Launch Keychain Access, go to the preferences, click on the 'Certificates' tab, and make sure both of the options are set to 'Off' and not 'Best attempt' or 'Require if certificate indicates'.

Turning these off, I was able to download updates with no problems.

This worked for me!

REMEMBER to put those two settings back where they were after your install is done!

I could install the hanging updates after deleting the appstore cache.

Open Terminal to open the chache folder using the command:

open $TMPDIR../C/

Delete the com.apple.appstore folder, then quit and relaunch the App Store application

the second time the installation worked.

You may not want to set the settings back. I came at this from my Console log - it was getting spammed with messages from secd (security related background program new in Mavericks) that made me go look at certificates and keys in Keychain Access, and I thought to turn those settings to 'Off' while I was at it.

I should have tested more - setting those to 'Best attempt' seems to allow things to still work. That seems to be the default setting, or at least is for the new admin user I created this morning to actually download the updates as per one of the other posts in here. In any case, I set them to 'Best attempt', deleted one of the apps I had downloaded from the store, and it allowed me to redownload it without any problems, so I think I'll keep it at 'Best attempt' for now.

It seems that some of Apple's certificates aren't finding a root certificate or some such, and if you have those settings at 'Require if certificate indicates', it causes them to fail when being verified. Or at least, I think that's what's going on.

These are the console messages (repeated over and over) from secd, in case anyone is wondering:

10/23/13 2:16:25.344 PM secd[229]: securityd_xpc_dictionary_handler Keychain Access[1335] DeviceInCircle The operation couldn’t be completed. (com.apple.security.sos.error error 2 - Public Key not available - failed to register before call)

10/23/13 2:16:25.345 PM secd[229]: SecErrorGetOSStatus unknown error domain: com.apple.security.sos.error for error: The operation couldn’t be completed. (com.apple.security.sos.error error 2 - Public Key not available - failed to register before call)

(So far, I haven't seen any more messages since changing the settings in Keychain Access, but I'm unsure of what exactly was triggering them in the first place.)

This is working for me, as well. Thanks!

This seems to have worked for me. (Keychain prefs)

I actually looked at my certificates and keys and noted several expired certicficates, as well as duplicates having read alll of your comments, so I cleaned both the certificates up and the corresponding keys, and set the preferences back, and viola, no more issues. While I am not completely tech savvy so i can't explain why, I can tell you that this worked, I will also say that I was very meticulas in getting the balance between the keys and certs right, hopw this helps, cheers.

Nice, the tip with the Keychain settings for certificates finally helped. Thx!

The keychain gambit didn't work for me with my original user identity (keychain crashed whenever I tried opening Prefs), but the new administrator identity allowed me to update all the apps. I then opened keychain prefs under the new identity, which worked and was set to Best already. After that my original identities keychain prefs did open, I changed it to Best attempt and was then able to installe a free app from the App Store.

I spotted Mavericks installation had added "allow guest user" (it wasn't optioned by me before I ran the update and was definitely there after). Just throwing that into the mix - I turned it off and then was allowed to update without the "Failed to verify the preflight file. It is not signed by Apple" error message.

Setting the options to "Off" in the "Certificates" tab allowed me, too, to download updates from the App Store. Now have them set back to "Best attempt". Thanks for the tip.

The Keychain solution worked for me. Thanks.

I tried the temporary user route and the keychain later. Both worked. I would suggest the keychain route first.

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