https://forum.emclient.com/emclient/topics/new/add_details?post_flow=true&topic[subject]=microsoft+account+not+authorised+error 
About 4 days ago the 2 microsoft accounts i have stopped syncing so i tried to add the accounts again and got this error. the accounts can be accessed with other clients and online but not emclient. I am using Win XP and Emclient 7.1.31747.0
For about 2 years eM Client has not been supported on Windows XP. That means that after the 30 trial period, you will not be able to activate a license to continue using the application.
Without a valid license eM Client will not sync with your email accounts.
About a year ago i had the situation that because i was using XP the new licence servers at Em client could not be synced because of how XP handled SSL .
I contacted Em client and they provided a download link to ver 7.1.31747.0 which was a one off version to enable XP to communicate with the licence servers. This setup has been working for a year until 4 days ago when all microsoft based emails stopped syncing.
I suggest you contact the eM Client employee who gave you the link for that version, and ask if there have been any changes with the XP policy that would have caused this.
Hello Martin,
From what I know, the specific build of eM Client 7.1 for Windows XP is having difficulty with authentication - based on the obsolete .NET framework. Unfortunately, this version is no longer developed or fixed so unless MS changes its authentication policy, the only option is to upgrade your OS.
Russel