OK it was a rewrite issue in the .htaccess file. The original setting for the Opencart sitemap had been setup to do some rewriting stuff lol I'm not sure what I'm talking about, anyway I commented it out and it is now working...
BUT.....
It only crawls the first page of each category unless I remove the page= from the exclusion list. But now as well as crawling all the product pages it also includes the paginated category pages which I do not want including.
So close to getting this right! How do I make sure it crawls all products under each category WITHOUT including the paginated category pages?