Installed and tested ERAS v.5 beta. At last they solved duplicate client names problem described here. Solution is very clever, if I correctly understand it. When client connects to ERAS and it's name already registered on ERAS but MAC address is different, server checks if this client have network card with MAC address already registered on server. If so, even if this network card is not connected to network, ERAS knows it's the same client and don't makes duplicate.