Error Connecting to iCloud

One or more of he Apple trust certificates have most likely expired. go here Available trusted root certificates for Apple operating systems - Apple Support then pick the OS for your machine click on the certificates to download, I downloaded all of them to make certain I got the correct one, after downloading it, double click on the downloaded certificate and it will automatically install to the keychain app. The reason for this is Sierra 10.12.6 is no longer being updated and once the original certificates expire the machine will no longer connect to the Apple servers.

Janeway3000 Said:

"Error Connecting to iCloud: [...]I am getting an error message 'Account Details could not be opened because of an error connecting to iCloud.' I also often get an error message while I'm online, saying 'Could not connect to iCloud' [...]Not sure what the issue is.[...]"

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Seems to be a Bug:

I have seen a few posts in regards to this just now. So, there may be an issue connecting to Apple's servers, on Apple's end. So, try this later on.

Solution found in another thread:

 « hello,

downloading this certificate did solve the Problem for me.

https://www.apple.com/certificateauthority/AppleISTCA2G1.cer

[This is a Direct Download Link] »

Here too:

https://discussions.apple.com/thread/253816134

iCloud service was disabled for iOS10.3.3… - Apple Community

Some were simply answered by @Apple that their devices or OS’es were too old and not supported anymore. Glad that someone found a fix but I hope that somebody @Apple is reading the forums for the last week. High Sierra, Sierra and iOS 10 are all affected by this iCloud bug…

Janeway3000 Said:

"Error Connecting to iCloud: [...]Thank you for replying and trying to help. I'll try again later. L But - I've also just deleted my macbook pro from my devices list in iCloud to try and reset it. Only problem is I don't know how to re-add it back now :"

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You are welcome.

You'd need to sign in to iCloud on it.

I am having the exact same issue. Wondering if its a bug with new Sierra update.

Please, would appreciate Apple to look into this on their end. I can't sign out of icloud, can't access my account details, notes isn't syncing with icloud, icloud drive also isn't syncing.

I'm using Sierra 10.12.6 on a mid 2010 iMac and I'm having the same issue and getting these messages.

Verification Failed

There was an error connecting to the Apple ID server.

You can't sign in at this time.

Try signing in again.

Thanks a lot, the problem was solved after updating the certificate.

Except that, when troubleshooting, I switched off and on for some items (such as `Notes`).

Many days of notes are missing now due to the operation above and the certificate problem (so there is no backups on iCloud).

See a thread iCloud account details could not be opened - Apple Community

Note : its not a bug , no issues from connecting to apple server Apple - Support - System Status

Hi. Read this thread and try the solution. It's been working for others.

https://discussions.apple.com/thread/253811711

Your issue is quite different , erase the hard drive and reinstall Mac OS .

In addition to my comment above the .plist is missing from ~/Library/Application Support/iCloud/Accounts/

Same issue, too. Now my Notes and iCloud drive are all empty, and I can not sign out of my iCloud.

My experience with Apple is once they have your $ they don't give a **** and couldn't care less. They'd rather have you go and buy their latest product designed for future obsolesce.

You're welcome I'm glad it work out for you.The missing notes issue also once happened to me so I no longer trust backups to iCloud and backup using using the timemachine app.