Recently Live Writer has stopped working for me when trying to post articles to my wordpress blog. The error that I keep getting is “Invalid response document returned from XmlRpc server”.
After a bit of digging and pointing fingers to all my installed plugins, I have found out that the problem actually comes from a very unexpected place – the BOM marker inside my wp_config.php.
If you encounter this problem, the easiest solution is to load the file inside Notepad++, go to Encoding and select UTF-8 without BOM. Save and voila! Live Writer works again.
For a more complete and detailed explanation check out this blog post: http://blog.scribz.net/2010/12/windows-live-writer-wordpress-unicode-bom-error/#more-22