PaulS:
Is the device really an RS232 device? The Arduino can not handle an RS232 device directly. The serial signals are the wrong voltage and are inverted. You need a MAX232 chip between the Arduino and any RS232 device to handle the voltage differences.
Using MAX232 to convert TTL-RS232 is more reliable and more consistent data than using SoftwareSerial (with inverted logic parameter), but then you cannot use Serial for debugging/monitoring.