Why can't I post comments on some blogs. :(

I've been to many blogs, which I wish to comment on, but it will not let me. They are always blogs that ask which profile to choose. I choose the google account, it loads the next page...then nothing, no comment, just back where I started. At first I was like, Oh well....but now, it's really bother me. Anyone else have this problem? What should I do?

I double check that I'm logged in. I also wanted to post a comment on my own blog, and it does the same thing. I must be doing something wrong. I even tried a second time to do it as anonymous. I am on a Mac, using Firefox.