arduino uno/mega to sabertooth 12x2

hey,

i’m working on a recyclebot, there for i would like to controll the motors through sabertooth.
I would like to connect 2 DC motors on it and control them separately through the sabertooth using serial ports.
The problem is that it won’t work, only the first motor gets his signal.
Maybe it is because the DIP switches are wrong, I connected them like this: on,off,on,off,on,off.
Here is the basic code i use for testing.

#include <SabertoothSimplified.h>
#include <SoftwareSerial.h>

SoftwareSerial SWSerial(NOT_A_PIN, A5); // RX on no pin (unused), TX on pin 0
SabertoothSimplified ST(SWSerial); // Use SWSerial as the serial port.
SoftwareSerial SW1Serial(NOT_A_PIN, A4); // RX on no pin (unused), TX on pin 1
SabertoothSimplified ST1(SW1Serial); // Use SWSerial as the serial port.

void setup()
{
SWSerial.begin(9600);
SW1Serial.begin(9600);
}

void loop()
{
ST.motor(1, 127);
ST1.motor(1, 127); // Go forward at full power.
delay(2000); // Wait 2 seconds.
ST1.motor(1, 0);// Stop.
delay(2000); // Wait 2 seconds.
ST.motor(1, 0);
ST1.motor(1, -127); // Reverse at full power.
delay(2000); // Wait 2 seconds.
ST1.motor(1, 0); // Stop.
delay(2000);
}

(the program i got from http://www.dimensionengineering.com/software/SabertoothSimplifiedArduinoLibrary/html/
and changed it a little bit)

maybe there is something wrong here?
or the sabertooth can’t handel two serial ports but that would surprice me

i hope somebody could help me.
Thanks in advance and greets,

Nel