Cannot get OpenID to work

Registering with OpenId does not seem to be working for me. What I did:
- enable openid plugin
- sign in with openid:
http://localhost/vanilla-2.5.1/index.php?p=%2Fentry%2Fopenid&Target=discussions
- enter
http://localhost/index.html
as openid URL. The file contains:
<link rel="openid2.provider" href="https://openid.stackexchange.com/openid/provider"> <link rel="openid2.local_id" href="https://openid.stackexchange.com/user/[my user id]">
I will be redirected to stackexchange and can enter by credentials. But the following error occurs after I entered a username under "Add Info & Create Account" after I am redirected to localhost when I click on "connect" ($openID
is an array, not an object):
I also tried entering http://[my id].openid.org.cn/
as openid URL, which results in the same behavior.
I am using Vanilla 2.5.1 and Firefox.
Am I doing something wrong, or is there a bug in the openid plugin?
Thanks!
0