What is this Fatal Error in the W3C validator?

Question

Search Engine Optimization

I decided to check my site for validity in validator.w3.org . Changed doctype from XHTML to Doctype HTML (html 5). In XHTML, schema.org markup was not recognized (there were about 40 errors). Changed to html 5 and here you are: Fatal Error: Cannot recover after last error. Any further errors will be ignored (screen - upload.akusherstvo.ru/image1239779.jpg , the photo does not load).
I understand the problem is again in schema.org markup. Removed code: itemscope="itemscope" itemtype="schema.org/WebPage". And then again fatal error (link - upload.akusherstvo.ru/image1239780.jpg ). I don't like file nesting.
Why is the entire list of errors not displayed, why are there these fatal errors, what should I do?

Answer 1

This is a piece of code for your site:

<a><ul class="post-categories">
  <li><a href="http://ravesli.com/category/uroki-s/" rel="category tag">Уроки С++</a></li></ul></a>

Link, there is a list in it, there is another link inside.
Of course, there will be a fatal error, because the validator did not understand one link, and here is a new one.
Carefully correct the mistakes one by one.

Answer 2

Fix structure!