Not sure whats wrong, but I don't like the image uploader on bnut... I can tell you how I upload images. It is faster, easier, and you can upload larger high quality images. Plus viewers don't need to be logged in to bnut to see the images.
1. go to
www.imgur.com (no account required)
2. Click "computer"
3. Select files to upload (you can select multiple images if you want). You can even edit the images (crop/resize etc.) within imgur.
4. Once uploaded, you will see the image and a series of links in a toolbar on the right. Copy the link under "BBCode (message boards & forums)".
5. Paste this link into your forum post. The image will appear full size once you submit the post.
6. If you uploaded multiple images, click "second image" at the top and repeat.
You can do the same through most image hosters (photobucket, flickr) but imgur is nice because you don't have to log in.
Hope some people find this helpful...