DD Sitemap Generator- Error 404

I have a nice looking sitemap on its own ‘sitemap’ page that works well apart from the last option of ‘View XML Sitemap’; when I click on this I receive an “Error 404 – Not Found” message.

I believe it is something very simple that I’ve missed; I have a feeling that it could be to do with updating the ‘permalink structure’ after changing the ‘Sitemap page slug’ as I am not completely sure what this means or what in fact I need to update it to.

On the other hand it could be something else equally simple.

Grateful for all advice, but please speak slowly as I am very much feeling my way here and am on a very steep learning curve!