Hi dodgeguy! Likely because the picture is too large. Pictures uploads are limited to 1024x768 unless you link them from another source. If your picture is larger than this, you'll need to open it in an image editing utility and scale it to below the limit if size is the problem.
A good open source (free) image editing utility is the Gimp. Once installed, go to File then open. Choose the image from your computer you want to edit. Once it is up, choose Image from the menu, then Scale. A utility will come up where you can change the image size which is fairly intuitive. After you've made the changes, choose File again and Save as. Name the newly edited file something different so it doesn't overwrite your original image. Then try to upload. Hope this helps.
