When using Chat Filtering in ContentBarrier to Block chats, your chat Application must be configured to not use a secure connection.
For example with Messages, the option to Use SSL must be disabled in the Preferences.
Click on the Account tab at the top of the Preferences window, highlight the account in the left column, and click the Server Settings tab below.
Uncheck Use SSL.
Once "Use SSL" is unchecked, close the Preferences window. This will allow ContentBarrier to block chatting with this chat account.