I've been having so much trouble lately posting comments on Google blogs and I'm very frustrated. However, I went searching for an answer and I found what we in Information Technology call a "work-around". (Well, when I worked in IT in the Dark Ages this is what we called it, anyway).
The Problem: When I leave a comment, I select "Google Account", and there doesn't seem to be another option to pick that works for me (i.e. I don't belong to any of the other accounts). At that point is where the problem starts; when I'm asked to log into my Google account I seem to go in an ever ending loop of logging in.
The work-around: Uncheck the "Remember Me" box in the log-in screen. It worked for me!