You have a Content Filtering policy to allow (or at least, no policy to deny) access to a certain website, but you are still receiving a Blocked result when trying to access it, usually stating that the webpage in question contains Spyware or other malicious software.
Many times, when trying to verify the URL in question with WebPulse Site Review Request, you won't see any abnormal result or malicious category.
This is because either the URL, or the IPs associated with it, are categorized under a malicious category ("Malicious Outbound Data / Botnets" or "Malicious Sources / Malnets", or "Placeholder" or not categorized at all, in case you are blocking unknown content and Placeholders)
To verify: