I was responding to a post yesterday and I kept getting that, too. I tried several times... but oddly enough, I typed a shorter message, and it went through. I see that 'sewmom' knows the answer. I'll try and keep that in mind.
I have had this some times too. So thank you sewmom for the explanation.
Too many characters in the first part of your question. Reduce the number of words. I have found that it happens when I post the freebie post but I don't know if it happens in other sections.
Also leave a huge space between the top part that I want to show on the front post and the body of the inner post.