Please ensure that the Barracuda Web Filter is running firmware version 7 or higher.
There are specific requirements as to how the traffic traverses the filters services and engines,
Please see these articles, above and below, for a chart to explain this better so you may verify if a
block page may or may not show up in your scenario.
Link to this page:https://campus.barracuda.com/solution/501600000013m2cAAA