Folks,
Here's what I did to solve this problem on my machine. I tried deleting the app and then reinstalling it, but I noticed that it didn't seem to be actually re-downloading the package. I became suspicious that there was a corrupted package cached locally, and that was what was being used each time I tried to re-install. So - I watched the console log while I reinstalled, and saw lines like this:
7/26/13 7:44:34.995 AM App Store[539]: PKDistributionController: Found asset mzps1920463678173855336.pkg on disk for item 403388562 - Size 9931864
So I searched my machine for any files called mzps*.pkg,
sudo find / -name 'mzps*.pkg'
and I found them in
/private/var/folders/1s/xrn3l0bd44x127w16mybylz877q2mf/C/com.apple.appstore
(I expect that path will be different on your machine - you'll need to run that find command yourself to locate the proper directory)
I then removed the com.apple.appstore directory
sudo rm -rf /private/var/folders/1s/xrn3l0bd44x127w16mybylz877q2mf/C/com.apple.appstore
restarted the App Store app, and then was able to successfully reinstall the original app. This also seems to have cleared up a problem I was having with two other updates being repeatedly applied. There were other (probably corrupt) pkg files in that directory that I got rid of.
Good luck!
-Colin
Message was edited by: cmurtaugh (fixed the rm command)