publish to book - missing pixels

when I've published a short document to PDF as a booklet (for printers pairs), the resulting PDF has missing pixels on pages containing one specific Illustrator image. Embedding the image doesn't help. The image in the inDesign doc hasn't been resized. The original Illustrator .ai file is compiled from a tiled vector pattern. The inDesign pages affected contain ONLY this image.Everything looks fine in Illustrator & inDesign - but a small number of white pixels (same pixels missing on all pages containing this image) in the published PDF. Any ideas anyone? This has to go to printer this week.