Some USB drivers are not Microsoft-signed. Restart your PC and press or use Shift+Restart → Troubleshoot → Advanced Options → Startup Settings → Disable Driver Signature Enforcement.
Before opening the utility, ensure your USB-to-Serial converter drivers are installed. Connect the converter to your PC and check Device Manager to ensure it is recognized (e.g., appearing as COM3 or COM4). Mstar Isp Utility V5.0.8 Download