If you keep getting the “Invalid Server Response” error when trying to publish a post to WordPress from Windows Live Writer, the possible culprit could be one of the plugins installed on your site and in my case it is Smush.it.
Finding the culprit plugin
If you haven’t made any changes to your site recently, to resolve this error I recommend that you disable installed plugins one by one and try publishing once after disabling a plugin. It took me months to figure out that Yahoo’s Smush.it is the root cause for getting this warning, it might be different in your case.
Here is the Invalid Server Response dialog:
“Invalid server response, the response to the metaWebblog.newMediaObject method received from the blog server was invalid. Invalid response document returned from XmlRpc server.” (see screenshot below).
Yesterday, after upgrading to WordPress 3.5, I was unable to publish a single post on my blog with images included in the post. While playing around with images in WordPress, I got an error related to Smush.it, which by disabling it, I was able to post the article without any issues.
Simple fix for error ‘There was an error uploading. Please try again later’
XML-RPC enabled by default in WordPress 3.5
And one more: from WordPress 3.5 onwards, you don’t need to enable XML-RPC to publish remotely from desktop blogging clients like Live Writer because it’s now enabled by default. And the XML-RPC option that existed in the Remote Publish to Write Settings section is now removed.
How to Configure Windows Live Writer for WordPress Blog
Say a reason to use Live Writer
Since the early days of blogging, I used to publish posts to my blog using Windows Live Writer, but lately that hasn’t changed.
If you ask me, tell me at least one reason to use Live Writer, here it is: one comfort with this tool I can say is that you can easily paste images directly into WLW, where you need to upload or drag and drop images to the WordPress.
Windows Live Writer shows “Recover unsaved changes?” dialog on startup [Reason & Fix]
Windows Live Writer 2011 Keyboard Shortcuts