The error message above usually occurred while submitting your sitemap file to Google's webmaster tool and this happens for several reasons.
First, the sitemap file you've submitted might be corrupted or not an acceptable format to Google's guidelines ( for more reference about sitemaps). Remember Google used html and xml formats. For convenience you can use the free sitemap creation tools online :
After creating your sitemap file, download it and upload to your site root using FTP. You can preview your sitemap file using the url : www.your site.com/sitemap.xml
|This is how the error looks like in Webmatertool|
Check now if you're be able to see your robots.txt file : www.your site.com/robots.txt, if not create your own robots file >> open a notepad then, copy and paste below text:
Save it as robots.txt file and upload to your site root.Now try submitting you sitemap again.
Third, the last issue is probably in your web hosting provider.Inform your web host to allow Google bot to access your site and this eventually works like a spell.
If you still had encounter the problem don't hesitate to put a feedback below and I'll try to help you.