Logged a bugreport: http://code.google.com/p/diso/issues/detail?id=65
It just occurred to me that, apart from WordPress configuration, hoster information might also be relevant. Unfortunately, I don’t know much, but I supplied all the information I knew and ready to provide more on request.
Yes, my mistake – I didn’t enable “Anyone can register” option. Now it’s fixed, you can try again.
But nevertheless: if you bumped into “non-existent user” problem, this means had successfully passed the authentication. Do you have an underscore in your OpenID name?
