I have 4 other games installed on Steam and all of them are able to successfully validate all files.
I've tried completely uninstalling and reinstalling the offending game to no avail.
I've also run the Disk Checking tools from my C Drive Properties Tools menu, as well as run "chkdsk /f" which runs chkdsk on boot, neither run showed any errors in the drive.
I've set my BIOS back to defaults with no overclocks and eliminated all but the essential services and programs from starting doing boot, including disabling my antivirus. I'm at a standstill with both Steam and Activision support, and I haven't been able to find anything with Google, so I'm REALLY hoping someone here might have some ideas.
I've already tried cancelling and re-validating before, to no avail.
OS: Windows 8 64 bit If after doing what you already did, you are left with deleting and re-downloading or hoping (rather blindly) that a future Steam update may fix the problem.
I've been aware of the validate steam cache files for a while.
It's unfortunate that it's the only option but perhaps you can let it download overnight.
If there are individual files you can narrow the issue down to that are not huge, try deleting them and re-downloading/verifying to see if it helps.
Steam support suggested it once and it got me out of a problem I had, so I try it again on occasion.
It appears to compare checksums of your local files with the cloud and will re-download any invalid files again.