Open Live Writer Can't Conect to My AV Blog Service

Open Live Writer used to work well with my Altervista blog.

But on my freshly installed Windows, I've installed OLW and it doesn't connect to my AV blog, showing this error no matter how many times I retry:

Can't connect to your blog service.
Server error...
403 Forbidden
...

Is it a temporary error, or AV has stopped allowing in other CMS apps, or something else is wrong?

P.S. I enter blog address, username, and password correctly.

Enable XMLRPC in WordPress settings.

Thank you very much Karl. Your guidelines have always been very helpful.