Network unreachable: robots.txt unreachable We encountered an error while trying to access your Sitemap. Please ensure your Sitemap follows our guidelines and can be accessed at the location you provided and then resubmit. [?]
I validated my sitemap with 2 tools and they seem to be okay. Sample of sitemap follows :
I am not a sitemap expert, but all a validation will tell you is that the XML is well-formed and conforms to a schema.
It sounds like your problem is actually with the contents of the sitemap. I'm guessing that the embedded URI points to a page/site that does not meet some follow-through requirement. Maybe the URI itself has a problem, or the robots.txt file has issues. I dunno.