Problem Simulink + Arduino

Hi there, I've got problems connecting Arduino to Simulink.

I am using MATLAB R2015a and Arduino Mega 2560 in order to control the temperature of a device. I established succesul connection between Simulink and Arduino, could save data to workplace and everything. I even created a PID control. But the problem is Simulink doesn´t let me re-upload the same exact control scheme giving the following error:

The call to realtime_make_rtw_hook, during the after_make hook generated the following error: The build failed with the following message: "C:/MATLAB/SupportPackages/R2015a/arduino-1.0.5/hardware/tools/avr/bin/avr-gcc" - -------------------------------------------------------------------------

The build process will terminate as a result.

The build failed with the following message: "C:/MATLAB/SupportPackages/R2015a/arduino-1.0.5/hardware/tools/avr/bin/avr-gcc" -

The only way I could get around this issue was to close MATLAB, open it again and trying again. Sometimes it works and sometimes it doesn't so I have to create a new model from the scratch, then it works OK and at some point it stops working.

Does anybody knows what's happening? Thanks.