It maybe popup an error message to say that “QI for IEnumVARIANT failed on the unmanaged server” when open the Windows Live Writer.
After search on google, I found the resolution is import some settings into registry.
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Interface\{00020404-0000-0000-C000-000000000046}]
@="IEnumVARIANT"
[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Interface\{00020404-0000-0000-C000-000000000046}\NumMethods]
@="7"
[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Interface\{00020404-0000-0000-C000-000000000046}\ProxyStubClsid]
@="{00020421-0000-0000-C000-000000000046}"
[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Interface\{00020404-0000-0000-C000-000000000046}\ProxyStubClsid32]
@="{00020421-0000-0000-C000-000000000046}"
You can also download the file ienumvariant_failed.zip, unzip and import it to your registry.