If you have a Blogspot.com blog and the Comments box is directly under the post, it won't accept comments from many of your readers. This is a glitch in Blogspot blogs that Blogger hasn't bothered to fix, so here's how to fix it yourself:
Go to SETTINGS in Dashboard
Go to COMMENTS
Go to "Comment Form Placement".
Change "Embed under post" to "POP-UP Window".
Change "Show Word Verification for comments?" from "Yes" to "NO".