Thanks that seems to have worked. This is what is needed.
In the file MyGatewayTransportEthernet.cpp around line 301 the following changes need to be made. All the [0]'s need to be removed.
Old:
#if defined(MY_GATEWAY_ESP8266)
_ethernetServer.read(inputString[0].string, MY_GATEWAY_MAX_RECEIVE_LENGTH);
inputString[0].string[packet_size] = 0;
debug(PSTR("UDP packet received: %s\n"), inputString[0].string);
const bool ok = protocolParse(_ethernetMsg, inputString[0].string);
#else
New:
#if defined(MY_GATEWAY_ESP8266)
_ethernetServer.read(inputString.string, MY_GATEWAY_MAX_RECEIVE_LENGTH);
inputString.string[packet_size] = 0;
debug(PSTR("UDP packet received: %s\n"), inputString.string);
const bool ok = protocolParse(_ethernetMsg, inputString.string);
#else