This is a classic data overflow issue. Change your software's flow control from Xon/Xoff to Hardware , or lower the Baud Rate to 4800 in both Device Manager and your software.

If you would like to optimize your setup further, let me know you use, your Windows operating system version , or the specific error message you are seeing. Share public link

If you want to troubleshoot a specific setup issue, tell me:

The SI 721 is commonly supported by the following professional cutting software: : Offers a dedicated plugin for CorelDRAW specifically for JinKa JK-721 EasyCut Pro

Searching for a "patched" or cracked version of a hardware driver carries significant security and operational risks.

What are you using with the plotter (e.g., SignMaster, Artcut, CorelDraw)?

When a computer fails to recognize the plotter, it is usually because the driver for this specific communication chip is missing, outdated, or blocked by Windows Digital Driver Signing. Why "Patched" Drivers Are Dangerous

The Ultimate Guide to SI-721 Cutting Plotter Drivers: Downloads, Fixes, and Alternatives

When you install the driver, you are not installing a driver for the "SI 721" itself; you are installing a driver that creates a (e.g., COM3 or COM4) so your design software can send vector data to the machine. Step-by-Step Installation Guide (The Safe Method) Step 1: Download the Core USB-to-Serial Drivers

If you see a yellow exclamation mark next to "USB Serial Port" or "CH340," note the name.