Preventing all resizing when uploading pictures

Hello, I tried searching the forums for an answer to my problem without luck.

I would like to prevent all thumbnail creation when uploading pictures through Wordpress media library. So for example when I upload a 1000x1000px picture, I end up having just the original picture in my uploads folder. Before I started using Atahualpa, I could achieve this by setting Settings->Media->Thumbnail, Medium and Large sizes all to 0 at Wordpress settings.

After installing Atahualpa, whenever I uploaded a large picture I ended up having the original, a 150x150 px and 400x1000 px resized pictures in my uploads folder. I got rid of the 150x150 thumbnail by setting Post thumbnails-> width & height to 0 at Atahualpa settings. The only thing I need now is to get rid of the 400px wide resized images. I can't seem to figure out which setting controls this.

I have tried disabling all my plugins with no difference. If I switch to a different theme there is no resizing. I'm using Wordpress 3.1 and Atahualpa 3.6.4.