Adobe CS4: Image too large to upload

I want to make a drawing using Adobe CS4 Illustrator and save it as a high resolution JPEG image. I will be uploading it to a dedicated photography website so I need to make it printable with 20×30 in size. I saved the drawing for photo and web device then upload it to the photography website. The problem is I keep receiving error stating that the uploaded image is too large and the quality will become blurry. Do you guys have any idea on how can I get rid with the error like this?
