I believe there is a known problem with posting between Blogger and Wordpress blogs (and vice versa). You can find the details if you search the web for them - but the answers are not always helpful!
I find that it helps if I am already logged into Wordpress before I start to post my comment - although that does not fix the problem everey time. Sometimes you have to resort to leaving an "Anonymous" comment, but you can always add your name at the end. Also, if I remember, I copy the text I've just typed (highlight then Ctrl+C) just in case the nasty computer imps delete it; then I can easily Ctrl+V it when I have another go.