Q: iMessage login authentication

Hi Cluelessonapple,

Sorry to hear that your having this problem, hopefully I'll be able to resolve it for you today. Try the following steps:

1. Go to System Preferences (choose the  on the top left corner of your screen).

2. Choose the 'iCloud' preferences pane.

3. Sign into iCloud at the OS X preference panel. If you're already signed in but still see the pop-up message, sign out then sign back in to stop that password prompt from happening again.

I really hope this works for you.

Have a good one!

<Edited by Host>

Messages – Can’t log in

Messages - Error Processing Registration

Hi,

It does not work because iCloud is nothing to do with iMessages.

In System Preferences > iCloud there is no entry for the following

Messages in any account form,

FaceTime.

iTunes,

iBooks,

Game Centre,

Messages CAN use and Apple ID as a valid AIM Screen Name (In System Preferences > Internet Accounts) IF...

it is an Apple Issued ID (@mac.com @me.com linked to iCloud.com and @iCloud.com ones themselves)

You may well use an iCloud linked Apple ID which is the same as the Apple ID used with the other servers but it is not part of what iCloud does.

There are circumstances that have happened in Yosemite (when Upgrading to it the first time) and El Capitan at the first version and the OS X 10.11.3 and 10.11.5 updates.

A random set of users seem to find their Apple ID used in Messages for iMessages from their Mac (And only their Mac) does not login any more.

The ID will work on other Macs fro iMessages.

It will work in the apps mentioned above.

iCloud and the syncs you have set up within that still work.

Only iMessages is affected on the Mac.

The Serial Number of the Mac is used to create a Device Specific Login to the iMessages servers.

It seems this Security feature can be triggered by mistake.

Testing in another Mac User Account can prove is is Mac wide and not just your Mac User Account.

Resetting the NVRAM may clear the issue is some cases.

Resetting using Safe Boot may also help.

The items in the links Eric has posted can also help.

If they don't then the ONLY fix is to call Apple Support (same as Apple Care).

Solving an Apple ID issue is free to fix.

If the Level 1 responder does not understand ask to speak to someone higher.

It can be a long drawn out process to get them to reset the Server so your Mac can use the Apple ID again.

They may want you to try things and do data gathering (they know of the problem but not what causes it - hence no released "fix").

Reinstalling, Upgrading or even Updating work.

It is a Server end issue.

People who have had this issue and gone through this and reported back say the engineers are often involved and they are told anywhere between 24 hours and 5 days for a reset.

9:47 pm      Saturday; July 30, 2016