False "500" error

Hello,

This morning (Nov 26/15) when I tried to use the Markup Validation Service (
https://validator.w3.org/) I got the error below:

500 Can't connect to spiritwoodontheweb.com:80 (Bad hostname)

I did not get the "500 Can't connect to ..." error when using Validator.nu.

I used the Markup Validation Service on Nov 24/15 and did not have a
problem.

I don't know if this is relevant ... I tried to validate three other
websites that share the same IP address as spiritwoodontheweb.com and they
too gave the "500 Can't connect to ..." error:

Name:    spiritwoodontheweb.com
Address: 173.254.28.112

Name:    ladymarmaladecafe.com
Address: 173.254.28.112
500 Can't connect to ladymarmaladecafe.com:80 (Bad hostname)

Name:    mary-crane-interior-design.com
Address: 173.254.28.112
500 Can't connect to mary-crane-interior-design.com:80 (Bad hostname)

Name:    robertworsley.com
Address: 173.254.28.112
500 Can't connect to robertworsley.com:80 (Bad hostname)

Thank you.

Lynda Tamasi