Blue coat web filter

Sometimes I try to get this web www.senavirtual.edu.co, but I get this message on the tab:

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Network Error (dns_server_failure)

Your request could not be processed because an error occurred contacting the DNS server.
The DNS server may be temporarily unavailable, or there could be a network problem.

For assistance, contact your network support team.

Your request was categorized by Blue Coat Web Filter as 'Education'.
If you wish to question or dispute this result, please click here.
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I use google to find the website, then I click on the link and website starts up.

what happen?

Greets