Just a guess, but I think you can't preview an attachment, since it doesn't actually upload till you hit "post".
possibly.
I'm just got very used to Greg's forum where choosing the file for attachment actually uploaded the file prior to making the post.
Yes, I'm one of those weirdoes that needs to preview my messages to ensure nothing is screwed up before posting.
The big downside I see to this forum's method is that you can't put spoiler tags on images that are being uploaded unless you go back and make edits after posting.
It'd be great to have all the upcoming ANS7 images hidden by spoiler tags, but I don't see that happening