Why do you think the errors are related to software serial? Why are you mounting a Wireless shield on a wired device?
How much memory do you have available?
http://playground.arduino.cc/Code/AvailableMemory
(Not enough would be my guess.)
char inChar = Serial.read();
if (inChar == '\n')
{
result[i] = '\0';
Serial.flush();
return 0;
}
Why are you calling Serial.flush()? Do you have a clue what it does?