Bad host name?

As of just two days ago, over 250 pages at these sites [www.tsujiru.net/compass] and [www.tsujiru.net/moen] were working just fine and validating for html 4.01 and CSS.

As of right now, none of these pages can be found by the WC3 validation service although all are available via HTTP.

For CSS, I have the following error message:

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I/O Error: The host name [www.tsujiru.net] couldn't be resolved. Details: www.tsujiru.net
###

For HTML/ XHTML, I have the following error message:

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I got the following unexpected response when trying to retrieve http://www.tsujiru.net/qatar/navigation.html: 

  500 Can't connect to www.tsujiru.net:80 (Bad hostname 'www.tsujiru.net') 
Please make sure you have entered the URI correctly.
### 

The web pages show up just fine, however, and the link shown on the WC3 page can be followed back to the original.

Please advise.

Thank you.