You need to have a basic understanding of game development. Games typically use textures that have sizes that are power of 2. That's what the error is attempting to explain.
In the case of NR2003, the height and width of your image needs to be a power of 2.
Some examples (in pixels):
512x512
512x256
512x1024
128x56
2048x1024
4096x4096 - I wouldn't try anything higher than this.
If this doesn't make sense, you might need to do a little bit of research.
You'll also probably need some sort of photo editing software. Gimp is usually a goto for open source (free) software. Create a new image with the dimensions of power of 2, and then paste your image in it. Resize or save the image that way and try it again.