This has worked for some:
- Sign out of the App Store (in the Store menu)
- Quit the App Store
- In Finder - Go>Go to folder... (or Apple-shift-G)
- Paste in the following "~/Library/Caches/ "
- It will take you to a folder. Delete com.apple.appstore
- Launch the App Store. Sign in and then reclick the Mountain Lion buy. It won't charge you again.
I deleted the com.apple.appstore cache, Relaunched the App store app, signed in again, downloaded it again, and unfortunately, I still get the same error message. I've now downloaded it more than a dozen times, each time with the same error.
Any other ideas?
My Pages updated, and now I can't access any of my documents due to Pages saying it now requires OS X 10.7 or greater...
Fantastic, I'm running out of ideas and patience...
These may be long shot suggestions.
Try creating a temporary user account with admin privileges and attempting the download using the new temporary user account.
Try booting into the Safe Mode and trying again.
Last suggestion is do you have access to another Mac computer where you could try to download the software and then transfer it to your computer using a flash drive? Make sure you use your Apple ID when going through the App Store to avoid future potential problems. If so, this might help.
If any of this is successful, post back and some further troubleshooting can be done.
Well, after trying more than 2 dozen 10.8.2 App store downloads, I was fed up and getting ready to load up the computer and haul it in for service/cleaning/hard drive replacement (mine was one of the recalled units), when I tried it one last time... and it installed perfectly!
Thank you both for the assistance. Since the install, all of my previous quirks and issues seem to be resolved.