Created attachment 6816 [details] specimen file The attached PDF file contains text in a /Separation space with a /DeviceRGB alternate space. PDF/X requires that colours be in DeviceGray or DeviceCMYK (or a CIE space) but when converted to PDF by pdfwrite the colour space maintains its alternate of DeviceRGB.
Fixed in revision 11849: http://ghostscript.com/pipermail/gs-cvs/2010-October/011889.html