Some Bloggers Cannot Post Comments

Good morning! I have posted this problem a few times without resolution, partly b/c we cannot pinpoint where this is happening. Now I can. Sometimes people cannot leave comments. The one follower that helped me pinpoint the issue stated that if she enters via the reader to my blog, she cannot post comments. If she enters my blog via typing in the url, she can leave comments. How can my readers leave comments via the reader?