when i running the simulink lego mindstorms ev3, the problem come out

Error occurred while executing External Mode MEX-file 'ext_comm': Failed to connect to the target. Possible reasons for the failure: a) The target is not switched on. b) The target is not connected to your host machine. c) The application for the model is not running on the target. You might have clicked the Stop button. If the Run button is not dimmed, click it. Otherwise, click the Build button, which downloads and runs your application on the target.

Caused by: An error occurred attempting to open an rtIOStream. More detail may be reported in the MATLAB command window