The default on-the-wire encoding for Ice changed in version 3.5 and IPv6 is now enabled by default. ABI versions are not compatible. For details on these and additional changes please read the upgrading instructions available at http://doc.zeroc.com/x/SQpN For on-the-wire background compatibility add Ice.IPv6=0 Ice.Default.EncodingVersion=1.0 to your Ice application configuration.