I am so fed up with these comment problems, first of all the pop up comments didn't even show a link on individual posts, which took a long time to work out after Debbie Moore kindly pointed out the exact problem. I posted about it on the blogger help forum, got no help so changed comments to embedded. This worked, comments were fine.
Then suddenly comments stopped working again, you could only comment if a comment had already been left on a post! Again I posted in the blogger support forum which seems to be the only way of reporting problems. Again this has been totally ignored, so I just changed comments again, this time to full page and it is working - at least for now!