@Danny: The Directory endpoints are available for configuration via the app config file: Microsoft.Exchange.AddressBook.Service.exe.config. Look for the RpcTcpPort key. The MAPI endpoint is configurable via the registry: HKLMSystemCurrentControlSetServicesMSExchangeRPCParametersSystemTCP/IP Port
You can also take a look at: http://technet.microsoft.com/en-us/library/ff625248.aspx ; section: Configuring Static Port Mapping for RPC-Based Services and http://technet.microsoft.com/en-us/magazine/ff626260.aspx
“Load Balancing CAS Arrays” section
@iamme: Not sure there may be a trust issue but I would need a lot more info/troubleshooting to determine the cause for this.