hehe its me again.Thx alot Paul for the guidance. I finally got it all working smoothly!!!!. only thing i did was to start reading the serial port after 4 bytes.
if (Serial.available() >= 4)
{ // Check if there is a new message
dirA= Serial.read(); // Put the serial input into the message
dirB= Serial.read(); // Put the serial input into the message
pwmMotorA = Serial.read();
pwmMotorB = Serial.read();