Unable to submit sitemap.xml

Let me start by saying, I tried submitting my sitemap.xml
unsuccessfully several weeks ago. Today, I didn't see any option to
resubmit, so I deleted the sitemap.xml setting from my site overview
and am now trying to add it back in.

I created a site map at http://www.qualitypetproducts.com/sitemap.xml
using a tool: phpsitempang. When put the above url into an xml
validator at http://www.w3schools.com/dom/dom_validate.asp, I get:

The file http://www.qualitypetproducts.com/sitemap.xml
Validated Successfully without Errors

So, it looks like the URL & xml are good. However, when I logged into
my Google Sitemaps, I am unable to add this URL to my account as a
"General Web Sitemap". I get the error:

"We couldn't find the Sitemap at the location you provided. Please make
sure the Sitemap URL is correct and resubmit your Sitemap."

Is there something I'm missing on configuring this sitemap.xml?

I appreciate any help or suggestions.

Dave