An unknown error has occured - Mac App store

I have had this same problem for several days now. I performed a clean install on two different mac computers and then attempted to log into the app store as soon as the desktop loaded for the first time after creating a new user profile. I get the error message when attempting to log into the Mac App Store with two different Apple ID's.

Launch the Console application in any of the following ways:

☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)

☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.

☞ Open LaunchPad and start typing the name.

The title of the Console window should be All Messages. If it isn't, select

SYSTEM LOG QUERIES ▹ All Messages

from the log list on the left. If you don't see that list, select

View ▹ Show Log List

from the menu bar at the top of the screen.

Click the Clear Display icon in the toolbar. Then take the action that isn't working the way you expect. Select any lines that appear in the Console window. Copy them to the Clipboard by pressing the key combination command-C. Paste into a reply to this message by pressing command-V.

The log contains a vast amount of information, almost all of which is irrelevant to solving any particular problem. When posting a log extract, be selective. A few dozen lines are almost always more than enough.

Please don't indiscriminately dump thousands of lines from the log into this discussion.

Please don't post screenshots of log messages—post the text.

Some private information, such as your name or email address, may appear in the log. Anonymize before posting.

When you post the log extract, you might see an error message on the web page: "You have included content in your post that is not permitted," or "The message contains invalid characters." That's a bug in the forum software. Please post the text on Pastebin, then post a link here to the page you created.

Back up all data before proceeding.

Triple-click anywhere in the line below on this page to select it:

/Library/Preferences/SystemConfiguration/NetworkInterfaces.plist

Right-click or control-click the line and select

Services ▹ Reveal in Finder (or just Reveal)

from the contextual menu.* A folder should open with an item selected. Move the selected item to the Trash. You may be prompted for your administrator login password. Restart the computer and test. If there's no change, restore the item you deleted from a backup, overwriting the one that may have been created in its place. Otherwise, you may need to recreate some of your settings in the Network preference pane.

*If you don't see the contextual menu item, copy the selected text to the Clipboard by pressing the key combination command-C. In the Finder, select

Go ▹ Go to Folder...

from the menu bar and paste into the box that opens by pressing command-V. You may not see what you pasted because a line break is included. Press return.

Credit for this solution to ASC member luis.pinho.

Do you have another Mac by any chance, and if so, can you sign in to the App Store on it?

I just helped a customer resolve this issue today, the workaround is to go to id.apple.com and temporarily remove two step verification from your account. You can do this form the password and security tab after you log in. You should then be able to log in to the iTunes store and afterwards can once again set up two step if you so desire.

I am hitting this as well:

10/5/15 9:30:12.641 PM storeaccountd[322]: XPC error for connection com.apple.backupd.sandbox.xpc: Connection invalid

10/5/15 9:30:12.990 PM sandboxd[143]: ([322]) storeaccountd(322) deny mach-lookup com.apple.backupd.sandbox.xpc

I have tried the whack of NetworkInterfaces.plist, a different machine, and confirmed I do not have two-step authentication.

I've seen in another thread to make sure my machine has a serial number (they both do).

Neither had this issue before El Capitan.

Same issue here, followed all advice i could find

reset NVRAM

delete network plist

delete appstore cache.

Some apps install just fine only 2 previously purchased apps that i've tried do not work.

Similar problem here.

I can log in to App Store and purchase applications but I cannot complete the installation for 1 application only (Mountain). In App Store I get "An error has occurred" message and in the Console I get "storeaccountd[283]: XPC error for connection com.apple.backupd.sandbox.xpc: Connection invalid" message, but no "... sandbox [] ... deny match-lookup ..." message as in described in the post above. I received Mountain Application Invoice by email and my credit card was charged.

This is what I have tried.

I used 1 MBP and 1 MBA. Each use 2 accounts, Administrator and Standard. All 4 accounts are connect to iCloud with the same Apple ID.

App Store on all 4 accounts show the same problem -> the problem seems to be with Apple / iCloud.

Nonetheless, I tried the following on the MBA using the Standard Account.

Log out App Store, quit App Store, disable two step verification, start App Store, log in and Install again -> not fixed.

Killed all "store" processes, deleted all "store" cache, reboot, start App Store and Install again -> not fixed.

Deleted

NetworkInterfaces.plist

Something I have not tried: Disable 2 step verification, disable iCloud on all 4 accounts, enable iCloud on 1 account and try to complete the installation.

I hope either the first patch for El Capitan or the major ongoing Two Step Verification upgrade will fix it soon.

I fixed the problem:

1) Start iTune

2) Agree on the new license agreement -> apparently it was a new version or it was the first time I used iTune after El Capitan upgrade

3) Log in with my Apple ID

4) Start App Store, go to Purchased and click Install