Among the moronic features of the TypePad platform is a bias against long comments. Please be clear:
I value long comments, but am in the grips of a mindless machine that doesn't.
The problem appears to arise if you've been typing in the comment window for a while. TypePad somehow decides that you're "idle," and when you post it rejects the comment, often with a perplexing message such as "we cannot accept this data."
The workaround appears to be: Copy your comment. Open a new browser window. Navigate back to the post and to a new comment box. Paste your comment. Submit.
I know, it's maddening. Let me know if you find a nonmaddening blogging platform.