How to use 'axf:printer-marks' with url option?

Hello,
        Antennahouse provides the following extension 'axf:printer-marks' which has an option to use URL that picks an external graphic file.The syntax I used is as follows:

<fo:simple-page-master master-name="..."
        xsl:use-attribute-sets="page-dimensions" axf:crop-offset="0.5in" axf:bleed="0.2in" axf:printer-marks="url(C:\...\...\...\...\...\CropMarksBL.eps)">....</fo:...>

I was expecting to see cropmarks from the graphic file on the corners of page but to my surprise I just see a grey border with 0.5in on all sides of page.

Is the syntax right? An example would help.

Also in the above fragment of code I just tryed to use one graphic file.How can I use four graphic files for four corners of page.

Thanks