An unknown error has occurred app store

HELPFUL, Idk why I can't rate it anymore but this worked for me.

I got a handed down Macbook Pro from my older brother, and it kept bugging me why I can't update OS X to MacOS. It kept on asking me to sign in, but it just kept on giving me errors like "Unknown Error (4)" or something. Turns out my brother's account was still signed in to appstore and I kept on logging in mine. so there, signed him out and logged on to mine. Done! THANK YOU SO MUCH!!!

Try this user tip > https://discussions.apple.com/docs/DOC-4133

If nothing there helped, disable anti virus software and turn off the Firewall in System Preferences > Security (or Security & Privacy)

Then try the App Store.

I've tried all of this now, logging in with different accounts, but nope! Still that "unknown error." I could contact Apple support but I would have to make a long distance call, do they have any email?!

Yes > Apple - Support - Mac App Store - Contact Support

Have you repeated the entire message; like was there a number following the 'Unknown error has occurred?

No there's no number, just "unknown error has occured."

Thanks for the link!

Make sure your system date and time is set correct.

I moved to Japan recently, but the date and time are set automatically.

I have the same problem. It is something that has happened recently and nothing has changed for my system. I just now went into iTunes and viewed my account using the same ID. That worked fine. Must be just an app store problem.

Yeah it works in iTunes for me too. I've contacted Apple support and they said I should remove the whole com.apple.appstore folder and try logging in again, but that didn't help either.

I am also having this problem...but only on one of four macs. My family has two iMacs and two MacBook Airs. The problem only appears to be on one of the iMacs. I have just contacted Apple Support by e-mail and "Albert" is pleased to be helping me....I'll post if we get resolution.

I'm having the exact same problem!

I am able to log in to the iOS app store and iTunes music store w/o difficulty on that computer. The problem is limited to the Mac App Store....is that the same with you?

Same! I can login to both with my Iphone, neither with my MacBook Air. This has been going on for well over a week. I've updated my software but, sigh, no dice.

I Have a same problem, i'm use my macbook air, i can login from iphone, itunes, but not work on app store. any solution for this ?