The new Mac App Store launched early Thursday morning, but not without a slight glitch. If you’re among the users repeatedly seeing the message, “We could not complete your App Store request. An unknown error occurred (100),” every time you try to download an app, you’re not alone.
What you’ll need to do is download an app — any app — in the App Store via iTunes, or one of your Apple devices with access to the App Store. Doing so will trigger the new iTunes Terms and Conditions to appear. They are, for some reason, failing to pop up for some users when they try to download an app in the Mac App Store. Then you’ll need to restart your computer and reopen the Mac App Store. (Some users say they merely had to restart the Mac Store or iTunes to get it work, but I had to restart my computer.) You should be able to download apps in the Mac App Store immediately afterward.
or what you can do is sign out on APPLE ID and sign in back.
