I got this error message a while ago, and suddenly none of my Mac App Store apps would launch, even after restarting the Mac. The App Store said that Tweetbot had been purchased on a different Mac, even though I had just downloaded an update for it minutes prior. Suddenly, I couldn’t even sign into the App Store app.<\/p>\n\n
Eventually I traced the problem to something that happened a day or so earlier. We’d had a thunderstorm that damaged my iMac’s Ethernet port (amongst other equipment). At the time, I’d just switched the iMac over to Wi-Fi and started researching surge protection<\/a> for my cable modem’s Ethernet output. All my apps continued to work.<\/p>\n\n But the Mac App Store uses the Ethernet MAC address<\/a> for verification, even when connected via Wi-Fi. At some point it decided to verify things again, and my iMac’s Ethernet was broken enough to interfere with this.<\/p>\n\n The solution, MacBreaker<\/a> explains, is a procedure to convince your Mac that it doesn’t even have an Ethernet port:<\/p>\n If neither of the above solutions fix the issue, open the System Preferences app and go to the Network section. On the left-hand column in the Network section, select each of the items and remove it by clicking the minus sign on the bottom of the column.<\/p> Then, go to \/Library\/Preferences\/SystemConfiguration<\/tt> in your main hard drive and delete NetworkInterfaces.plist<\/tt>. Or alternatively, drag it to the desktop (as a backup, in case things go wrong).<\/p>\n By removing all of the Network items in System Preferences and deleting NetworkInterfaces.plist<\/tt>, you have effectively reset the network configuration for Mac OS X. Reboot (you may have to reconfigure your internet connection afterwards).<\/p>\n<\/blockquote>\n\n This worked for me. I was able to sign in and download new Mac App Store receipts tied to the Wi-Fi MAC address. And they continued to work after I started using an external Ethernet dongle.<\/p>\n\n Note: OmniFocus also uses the MAC address as a syncing identifier. After completing the above steps, it will see your Mac as two separate computers, one of which is no longer syncing. You’ll have to remove the Ethernet one or else syncing will get slower and slower because it can’t generate a new baseline without hearing from that Mac.<\/p>\n\n Previously: More Mac App Store Certificate Problems<\/a>.<\/p>\n\n Update (2017-10-06): Howard Oakley<\/a>:<\/p>\n It also bears pointing out that, in the event of a sudden loss of the Ethernet port, one of your first actions should be to ensure that port is properly connected to a network, and to restart in hardware diagnostics or AHT, as detailed here<\/a>. You’ll also need to be within range of an active WiFi network, or you may find that you get a code CNWxxx reporting a WiFi hardware issue, rather than another error (unspecified, possibly CNxxxx series) pointing at the Ethernet port.<\/p>\n\n