If you are having issues posting comments to Blogger blogs, I found this information in the Blogger forums:
1. If a blog's comment form takes you to the log in page, UNCHECK THE BOX THAT SAYS "REMEMBER ME" and log in. It will take you back to complete your comment.
2. If you have the embedded below the post comment form, CHANGE TEMPORARILY to either the pop-up form or the whole page form. When the underlying problem has been resolved, youw ill be able to change back.
Hope this helps!