You are trying to access a certain site that should be allowed, but instead, you are getting a block page along with the error message "dns_lookup_failure"
Getting "dns_lookup_failure" error when trying to access a site through Web Security Service (WSS).
This is caused by an improper use of DNSSEC configuration. When WSS detects that a site being accessed is using DNSSEC, it must be correctly set up. If WSS finds any misconfiguration or issue with DNSSEC, it will automatically reject the connection.
You can check the DNSSEC status of a site with this tool.
NOTE: This is a 3rd party tool and it does not have any kind of affiliation with Symantec.
Web Security Service
To correct this issue, you will have to contact the administrators of the site and have them correct their DNSSEC setup.