Arduino Serial communication in simulink

Hey! I have a little problem, I have a Simulink program running on my Arduino. This program on my Arduino receives data from Simulink (PC) and transmit data back to Simulink to my PC. Sending a data vector of uint8 from my Arduino to my PC is working perfect, I only use a MUX and the Serial transmit block from my support package for Arduino.

The problem is, I can't read a data vector of uint8 on my Arduino what I am sending from my PC. I tryed to use the serial receive Block from my Arduino library and a DMUX... but that is not working. Can some one help me??