Simulink hangs on visualising data in a scope from Arduino Mega 2560

Dear reader;

Most of my Simulink models for the Arduino Mega 2560 hang after a successful download upon connecting to the target, though some of them work.

The external mode does work with certain very simple models.

i'm using a module that read datas from an MPU9150 sensor with s-function + matlab filter + saving all datas into the workspace + calibration block + integration block + 6 scope to visualise all the dats in the different axis ... . The exact procedure goes like this: the building process is successful, and it says " Model Successfully Downloaded to Arduino Mega 2560 ". But then, when running in external mode and trying to view data in a scope it functionne well but after i move the sensor i got the change in the values but after a while it freezze --> matlab freeze so i have to close it and re-open it again wich take a lot of time in every hangs on.

Details:

MATLAB Version: 8.2.0.701 (R2013b) Operating System: Microsoft Windows 7 Java Version: Java (build 1.8.0_31-b13) Board: Arduino Mega 2560 Fixed Step Discrete Solver (0.03 sec) External mode enabled. Baud rates 9600 Computer toshiba satelite L50-b

Any help would be much appreciated.

thanks