The SBS Support Team in Las Colinas announced that SBS servers may lose connectivity with a SBS 2008 server when a driver that uses TDI has been installed. TDI (transport driver interface) is being phased out, but is still used in third party security products such as Trend Micro's server product.
MS has a hotfix, but it has not been regression tested so only install it if this directly affects you. Download the patch here. Per MS, use the Vista 64-bit version for SBS 2008. For the SBS Team's complete article , click here.