A Tale of two accounts on the one computer running Windows 7 ultimate and Windows Live Mail Version 2012 (Build 16.4.3528.0331. With one Microsoft Account, an outlook.com email address sign in, all mail on WLM is synchronised as are contact and the calendar.

On the second MS Account, outlook.com email address sign in, the mail and contacts synchronise. However calendar does not sync and this message appears 'There was an error when attempting to connect to the Windows Live Calendar service. If the error persists, check to see if there's an upgrade of Windows Live Mail available or contact a service representative.'. Despite repairing and re-installing WLM  with the latest version this message continues on each of two desktops and one laptop (all running Win7) that I've tried. However I have found that the options available for the calendar include a line that 'Registered email addresses for calendar notifications'  and then a setting to add another email or remove one. This setting is not available in the account that doesn't work but you can add an email address using Microsoft Account where both accounts have the same look and options. Also settings in Outlook are laid out differently and more options are apparent on the account that works. Screenshots are shown. I would welcome and input to solve this mystery as it is quite frustrating, and something I can't fathom. I have checked all other settings and both accounts have the same region and time settings and run on the same software.  The above screenshots show first the working outlook account options for calendar and secondly the non sync account -note the more limited options and information