I/O Error: Connection reset

While trying to validate this page, I get the error of a connection reset.

http://24.15.124.241/webjobs/onepagesite/

 

Can you explain please the error, and why I am getting it, what I should
possibly change.

 

The CSS external file validates fine, but the page itself does not, though
it validates strict HTML.

 

I would like to have my page validate CSS, which it did until recently, but
I am unsure what change happened that caused the connection reset.

 

Thanks in advance.