As you know, HIPs has many components. I'm not sure if you have already, but have you tried isolating the individual components of HIPs to determine the component causing this issue?
Please go to the McAfee Service Portal HERE and click on "Search The Knowledge Base". Search for article KB54960.
This article will guide you through component isolation. It may take some time but it could lead to you being able to confirm exactly what the cause is.
Hope this helps.
Thanks for your reply Mo. We have already isolated the problem as being a firewall issue. The problem ocures with only the firewall component enabled, and not if it is disabled.
By the way Mo, you have been one of the many support engineers that have been involved in trying to find us a solution.