Windows 10 Pro 64 bit
I have a number of accounts (Outlook, Gmail and Yahoo) included in my Windows Live Mail. One of the most useful properties of WLM is to be able to view a list of all recent mail from all accounts in one list. Microsoft recommend using the Windows 10 Mail App. However, this does not contain this feature.
Anyway, I trustingly patched my WLM with KB3093594 and promptly experienced the same result as Banger696.
With fingers crossed, I uninstalled Mail from my Windows Live installation and then re-installed it from my old .exe file.
To my relief, all my accounts instantly reappeared with all my emails. All now seems to be OK again.
I strongly advise others to leave KB3093594 well alone at least for now. Hope Microsoft don't totally mess up Windows Live Mail 2012 in the future.