Issue: I was trying to send a mail from command line (or system call, same error) and got a WLDCore.dll missing.
Clicking an email link in a browser won’t work too.
Observation: Other ways, Windows Live Mail works just fine.
Resolution: Well, apart from uninstalling/reinstalling, search Registry for junk, search Microsoft.com for advices on antivirus/malware checks 😉 and obviously, updates, you only have to copy 1 dll file form an existing folder to the Live Mail folder:
c:\Program Files (x86)\Windows Live\Shared\wldcore.dll
c:\Program Files (x86)\Windows Live\Mail\
Done, integration is OK now.
If Live Mail is open, you have to close/open it again.