- The output you get from Windows Live Writer is not XHTML, i.e. unclosed br and img tags.
- When you’ve setup your blog in Windows Live Writer, you have used a version older than Beta 3
- Your blog’s style couldn’t have been detected by WLW
- Your blog’s style was been detected correctly, however you do not have a valid XHTML DOCTYPE declaration in your blog
Setting XHTML output manually:
||Edit Weblog Settings
Thanks Mr. Joe Chang, from the Windows Live Writer team, who have pointed that out for me.