Hello James,
it could depend on several factors, most often not related directly to JSitemap component but for example to sh404sef configuration or other extensions installed. Of course i assume that you are submitting the correct link for the XML sitemap and not the link for HTML sitemap.
By the way your version is too old and your subscription is expired on 28/07/2015
So you need to get the latest version of JSitemap and update it in order to ensure all working properly and receive support. You can contact me at
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All the best
John