Yeah, I tried to "upload" an image (16k) from my drive into a post and it DIDN'T work. I tried to edit my post and it won't let me re-upload an image. Then I figured out to post the image to my personal webspace and put the URL inside the {IMG} {/IMG} tags in the post.
If you forget to attach the file the first time around, it won't let you attach it when you edit the file. Has happened to me a few times.