Hi jools47,
I am one of the developers in Auctiva. Preview page should have nothing to do with the eBay token as long as you have a valid Auctiva account and it doesn't need to communicate with eBay to generate the preview(Sorry, Mike, you are wrong this time :-) ). jools47, could you tell us more about how it happened? Have you ever succeeded in generating a preview page at all? What browser were you using? Does that "blank ebay page" have any other information like title, start price besides the category?
Could you fire a support case regarding this issue? Please include as much information (description, images etc) as you can in the support case so that we could regenerate the error. Your help will be very much appreciated.