Please see this thread: http://www.talkgraphics.com/showthre...export-problem

In summary:
Exporting a XAR file with one of its layers' properties set to "Background layer (will not print)" results in that layer not appearing in page 1 of the exported PDF (as expected) but appearing from page 2 onwards in the exported PDF document (i.e., not as expected).

Additionally:
After exporting as PDF, an error box appears declaring that there was an error opening the PDF. The exported PDF seems intact, as Acrobat reports no errors upon opening it (except for the unexpected appearance of the non-printing XAR file layer from page 2 onwards).

The XAR file where this behaviour was initially seen is not complex. It comprises two optimised JPGs on page 1 and one optimised JPG on page 2, with a few lines of text (labels for the JPGs, and a header and a footer) on each page, and then a few lines and rectangles on a layer set as background to aid positioning of the images. Text lines (except for the image labels) and the background layer are repeated on each page, and each page subsequent to page 1 is a clone of page 1. The same behaviour was seen in other similarly constructed XAR files with more pages. The group of XAR files are, incidentally, part of a catalogue of items.

Versions of software are given in the original thread.