I am getting many of this every once in a while on different guests and IPs.
The action is:
?action=login2
After tracking some IPs, it came from various engine search; Google, yahoo and some comment spammer
That's an OpenID error when people are using the wrong information to log in via OpenID - or they're using the newer specification of OpenID that SMF doesn't support.
Reopening it as this is getting annoyed showing in my error log.
I have this all over my error log now, and I don't believe that I have people using the OpenID feature.