The product distribution file could not be verified. It may be damaged or was not signed.

so u sucessfully installed Mountain Lion?

I've sucessfully restart the download without the previous error message. For the moment still pending 5 hours estimate download time before the installation.

Regards

Deleted file com.apple.appstore in /var/folders/, dissabled VirusBarrier X6: problem solved!

Day two for m trying to get Mountain Lion from the App Store... Everytime I click "buy" I receive an error message :"The product distribution file could not be verified. It may be damaged or was not signed."

I tried a bunch of things but nothing seems to work. And for JOWIS... I don't believe I have com.apple.appstore file on my machine or the directory structure(/var/folders). I tried to disable Virus Barrier X6 but it still gives me the same error message in the App Store...

I had the same issue for the past two days, finally tried the suggestion to restart computer in safe mode. I did that, I'm currently downloading Mountain Lion (just over 2GB so far). Knock on wood that solved my problem.

These messages are probably due to Gatekeeper, a script warning on unrecognized apps as an additional protection. Some apps must be added a small script allowing to recognize this new feature.

Safe mode restart And do the download in safe mode definitely solved this issue for me. When the download have been finish i restart my MacBook pro normaly and I've been able to create a bootable USB key to install mountain lion on the 3 laptops me get.

I called Apple Support (because I'm brand new to the Mac World and thought I might have done something wrong). The tech that I spoke to put me on hold for a few minutes and went and talked to a supervisor.

The supervisor said that we are getting this message because the Servers handling the download are being overwhelmed. They recommended trying it at different times or wait a few days until the demand drops off.

I'm going to try the boot in safe mode since a couple people said that worked for them.

I shut down and rebooted in safe mode.

The ML update is now downloading with no problems. HUGE download so it will take a few hours but it is now downloading.

I tried your recommendation, did the repair disk permission, and I guess I needed to that coz the list of repain was quite long, HOWEVER, after I finished I tried to download ML, I got the same error message as before. no luck.

any news from anyone else guys? thank you

I concur, reboot in safe mode, download ML started smootly, but also, HUGE file, am not sure now long its gonna take.
thank you guys

Ok, I was having the same issue, tried everything and nothing worked. I finally stumbled upon a post from ifixit or mac fixit and they said:

"Another approach that is working for people is to clear out caches and other temporary files used by the App Store. To do this, open the Terminal utility (in the /Applications/Utilities/ folder) and run the following command:

open $TMPDIR/../C

A Finder window will appear that shows a number of folders. Locate and remove the folder called "com.apple.appstore," and then try launching the store and purchasing Mountain Lion again."

I tried this and bam! It started downloading with no issues. All I did was remove the folder to the trash and then emptied the trash to make sure the file was NOT present anymore. I hope this helps.

I had the same problem. Spoke to Apple support who directed me to Itunes support. Frustrating to say the least. Some have said remove virus barrier. I did and still nothing. Some posts have said to delete App store. DON'T DO IT.. App store is tuff to get back. This did work for me. Go to Finder, then go, pick go to folder, type in, /var/folder, and delete (send to trash). There were 2 folders I had to delete, KX & XX, and as soon as I sent them to the trash they returned but I was able to download & intall Mountain Lion and working well. Good luck..

I had the same problem:

ERROR: The product distribution file could not be verified.

I rebooted into safe mode (press start button, wait until boot-up sound, press and hold shift key until Mac symbol and loading symbols show, then release). Then loaded App store, downloaded a free app, which worked fine. Rebooted normally, loaded App store and it seems to have cured the problem, successfully downloaded Mountain Lion. I left everything, including Virus Barrier X6 running with no problems.