There's a known problem with Blogger/Blogspot blogs that some people experience a lot of trouble posting comments on them. The forums are FULL of complaints, though I haven't heard of an official fix from Google.
Personally I don't get any more errors posting on Blogger blogs than I do on Wordpress or any other kind. I suspect part of the problem is with how people's internet browsers are set--and I found a *fix* for that once too, but can't find it at the moment.
One of the easiest solutions is to have pop-out comments like I have, but it's not a solution in all cases--I gather it just solves the problem most of the time. And I did find one person who complained that in their firefox broweser the popout window is super teensy small and annoying.
I just found two other solutions, which require the owner of the blog to make a fix. I'm going to post them here for any blog owners who want to play around with them, though I won't be adding any instructions/visuals cause I'm off to bed soon (my exciting new bedtime of 3 AM instead of the horrid bedtime which had crept up on me of 8AM!)
But I might make a better post in future, if anyone wants.
So without further ado, the two fixes I just googled up, that seem to work for a lot of people:
I had the same problem, even though I had the option checked for people to be able to leave comments. I went to my Layout Settings, then "Edit HTML," and clicked the "Revert widget templates to default" underneath the text box. That took care of my problem...hope it works for you too!
I finally figured it out. Changing the settings like -emnj- made it so the posts I do now people can comment on but I couldn't figure out how to get it to change on the previous ones. So what I did was click on the edit icon for the post that no one could comment on. Then under the box I write in there is a part that says "Post Options". It's right above the orange "Publish Post" box. Click "Post Options" and click "allow comments". Presto change-o people can comment now.
#2 Explained on this person's blog, with proper detailed instructions: