Error 8020: Error reading comm device

As described by Microsoft, this error message is the result of a defective serial port device driver. It should be resolved by by obtaining an updated device driver from your serial port or USB adapter manufacturer.

Windows 10

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Some USB devices that emulate serial ports employ the usbser.sys driver. Unfortunately, the version of usbser.sys included with Windows 10 is defective; as a result, DXLab applications running on Windows 10 report an 8020 error when they attempt to communicate with such USB devices. There are two ways to correct this:

  1. switch to a USB device that doesn't employ usbser.sys
  2. replace usbser.sys with an older version that is free of the defect
    1. download an older version of usbser.sys from

    2. replace the usbser.sys file in Windows/System32/Drivers with the older version downloaded in the previous step; this may require changing security permissions by right-clicking the entry for usbser.sys in Windows Explorer, selecting Properties, and then selecting Security

    3. disable driver signature verification, as described here

    4. until Microsoft corrects the version of usbser.sys in Windows 10, repeat steps 2a through 2c after each major Windows 10 update

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ErrorCode8020 (last edited 2018-07-11 04:16:43 by AA6YQ)