As an alternative you can also try our non-DTD-based validator.
The Markup Validator tool can be found under Diagnostics & Tools in the navigation menu.
You should be able to find the errors in the document and correct them without too much trouble.
Make sure you eventually arrive at a file that validates successfully before you move on to submitting the Sitemap to Google.
Validation is an important part of the Sitemap submission process because you'll only be wasting your time if you submit the Sitemap and Google can't process it.
Because Google doesn't immediately process Sitemaps, you may not know that the Sitemap failed to process for several hours after submitting it.
The purpose of this tool is to help you understand if you have implemented your selected structured markup language in a way which allows Bing to read the information properly.