Hi Fumi,
I was running into the same error when trying to deploy my model to hardware after previously running it successfully on external mode. I was able to resolve the error by changing my active configuration set. To do this:
1) In your Simulink model, go to View > Model Explorer > Model Explorer
2) In the left "Model Hierarchy" pane, select your model.
3) In the middle pane, see if "External Mode Configuration" is active (the icon will be green). If so, right click on the other listed configuration, and select "Activate". For me, this other configuration was just named "Configuration". This is what my model explorer looked like after activating the other configuration set:
4) Once I changed the simulation mode back to "normal" and tried building my model, the error was resolved.
Hope this helps!
-Julia
