What file format and colour space is the image you used for the cover? What are dimensions of the image?
The cover file is a JPEG 378 x 584. I'm not sure about the color stuff; I didn't create the image.
It could be that it's in CMYK when it should be in RGB.
Does the file name have any strange characters in it?
The file name is numbers (the book's ISBN number) + "_frontcover". So... "xxxxxxxxxxxx_frontcover"
It should be in RGB? I've heard of these color type distinctions. Maybe that's the problem. Do you know if there is a way to convert it?
You can use Photoshop to convert it to RGB. There are open source alternatives like GIMP - which is free. But I recommend Photoshop - yo ucan get a free 30 day trial.