There is no blog linked to your WordPress.com username.
You did not provide the URL starting with http:// for the blog that you were trying to comment on.
Here’s how to link your username to your blog in your blog Dashboard -> Users -> Personal Settings -> then scroll down to Account Details. Then scroll down to where it says ‘Primary Blog‘ select the URL for your primary wordpress.com blog and then save changes.
Now every time you sign into the forum we can all click on your username and your blog will be linked to it. And every time you leave a comment on a blog your username can be likewise clicked and your blog can be instantly located.
Assuming you do have a WordPress.com blog, your login is only effective when posting to free hosted WordPress.com blogs. It's not effective when you post to WordPress.org installs. Read this please > http://support.wordpress.com/com-vs-org/
Trying to post comments on Blogger blogs is a drag. Open ID fails more often than it works. Blogspot software thinks we all have a single username here at wordpress.com and a single blog by the same matching name. It will not accept any other URL. So if we have a domain or more than one blog registered under the same WordPress.com username trying to comment becomes impossible.
Unless the blogger chooses to enable commenters to post with a username and URL on their Blogger blog it's next to impossible to leave a comment. The only workaround is to register a Blogger blog which will allow you to comment but your username will not be linked to your WordPress.com blog when you do.