Microsoft has been investigating an issue that affects all Windows Server 2008 products, but is shown up more so by things like Trend WFBS 5.1 and other antivirus software. The issue is that anything that uses the common firewall driver in 2008 will be affected. SBS2008 servers may start to have Active Directory errors, issues accessing the server via RDP and a variety of other errors. All this will start after 5 to 7 days. The only workaround so far has been to schedule a reboot of the affected server every 5 to 7 days.
It’s important to note that the issue is NOT to do with TrendMicro products as it happens also with other AV vendors as well. It’s a Microsoft issue and they have been working hard on resolving the issue. Microsoft have now released a hotfix for this which you can obtain from the URL below. The MS KB 961775 is not available just yet but should be out shortly.