I copied the link to the solution at Microsoft after translating it into english (now in bold print). Here it is and it worked for me, after spending an hour searching unnecessarily with Videotron tech support whose fault it wasn't. I also got a few dozen previously deleted messages reappearing in my inbox and sent box. In all the previous upgrades to WIN10, there has never been a snag with Windows Live Mail.
Windows Live Mail (2012) error 0X800C013E after installing WIN10 feature 2004
Close Windows Live Mail.
In the registry under
Computer \ HKEY_CURRENT_USER \ SOFTWARE \ Microsoft \ Windows Live Mail
create these 3 DWORD entries (I didn't have them) or change them to 1 if available
RecreateFolderIndex = 1
RecreateStreamIndex = 1
RecreateUIDLIndex = 1
Restart Windows Live Mail. Then the message display goes back to normal for me and the 3 values in the registry are reset to 0. Can be left like this.
For me, the account display in WLM with several accounts after the Windows Update 2004 was corrupt. This is also fixed.