Strange error when generating C code from Simulink

When I tried to generate code from a recently updated Simulink model, I got "index exceeds the number of array elements. Index must not exceed 0". This error happened only during code generation, not when running the model. After spending a day, I found out that the reason was forgetting the folder separator "\" in an entry in Model Configuration Parameters > Code Generation > Custom Code > Source Code list, i.e. instead of "abc\file.cpp" the entry was "abcfile.cpp". A very unhelpful error message for such a simple error... A better error message would be "could not find file abcfile.cpp".

By the way, you can generate code from the MATLAB command line with slbuild('your_model_name').

Another error is "Invalid setting for input port dimensions of ...". If you are sure that there is no problem with port dimensions, close MATLAB, delete existing .mexw64 files, open MATLAB and regenerate them.