Is the maximum file size for epubs sold through Barnes&Noble (via a publisher account) still 600MB?
I appears that the limit is now 20MB
Your manuscript file must be less than 20MB in size and in one of the following formats: .doc, .docx, .txt, .rtf, .htm, .html, or .epub. Many manuscript files that are larger than 20 megabytes don't need to be. If your manuscript file is larger than 20MB, try reducing the image size, decreasing the dots per inch (dpi), and/or increasing the JPEG compression on the images in your eBook. After applying JPEG compression to the images, you should be able to get the individual image files under 100 kilobytes each.
See also The Nook Press Publishing FAQ