When an internal error occurs during simulation of a System Generator model, an internal error will continue to occur even after the offending issue is corrected.
This error is due to a known issue with System Generator for DSP.
If this problem occurs, you must close the model and open it again to eliminate the error message. In some cases, you might need to relaunch MATLAB as well.
This issue is resolved in System Generator for DSP 11.2.