Blogging tools (like Windows Live Writer) stopped to work with my WordPress blog

I have a WordPress blog published at https://wp.qmatteoq.com.
I always used Windows Live Writer to write posts for my blog: a few weeks ago, suddenly, the tool stopped to work.
Everytime I try to publish a post I get the following error:

Invalid server response – The response to the blogger.getUserBlogs method received from the blog server was invalid. Invalid response document returned from XmlRpc server.

I’ve tried also to remove the blog from Windows Live Writer and configure it again, but I get the same error. The same situation happens with all the other blogging applications (both desktop and mobile) I’ve tried.

The problem came out from nowhere: it didn’t start after any particular operation and I’ve changed nothing in blog configuration.

Do you have any idea what’s going on?

Thanks!