Intego’s VirusBarrier X6 is a popular antivirus program for Mac computers offering protection against malware, trojans, viruses, etc. Unfortunately, this antivirus application doesn’t seem to like Apple’s Mac App Store.
Many folks have claimed that VirusBarrier X6 prevents downloading OS X 10.8 from the App Store. If you are using this antivirus, head over to the Mac App Store and try to download any app, game or go ahead and buy OS X Mountain Lion — you will get an error message saying:
The issue can be fixed by disabling VirusBarrier X6 or completely deleting it from your Mac computer. Follow the instructions to get rid of this program.
Close the Mac App Store.
Follow the instruction available on Intego’s website. Download the uninstaller and run it on your Mac to delete VirusBarrier X6.
Relaunch Mac App Store. Try to download OS X Lion or any other apps.