The product distribution file could not be verified

It might be tricky to pick apart the failure with caches being deleted.

One thing that always works for me is to boot to a USB drive with a clean OS and sign in to the App Store. If I get a failure there, I know the problem is on Apple's side or in the network.

If not, I have the app and know my system / library are not helping and can take action there once I'm sure the issue is with my customizations and specific install and not a server issue.

I have resolved the issue by retrying on (yet another) network. I had previously tried two networks, one of which was my home network, but it seems all of them had some sort of issue. On a different network today, it worked fine.

I think that the solution was to boot it in safe-mode, but I cannot be sure.

This answer did not help me, and it took four apple support techs before I got one (iApps) who figured out the drop dead simple answer. This answer does not apply to the above problem, but it has the same error message, so I'm posting it here for the next person who has an equivalent problem.

This error message seems to be the last ditch answer from the App Store when it does not recognize something that is too new for it.

We could not complete your update. The product distribution file could not be verified. It may be damaged or was not signed.

For example, on Yosemite, I cannot open .pages files sent to me from users who are already on El Cap. When I try to upgrade Pages, as it suggests, I get this error. The only way around it is to upgrade to El Cap so I can upgrade Pages. Not ready to go there quite yet, so I'll just ask for the files in some other format for now.