If it is indeed a USB communication error as others have suggested, have you tried using a different USB cable between the NanoVNA and PC? Maybe even try a different USB port on the PC. Are you connecting to an older USB-2 port, or ¡®newer¡¯ USB-3 port? Some software and/or hardware can act unpredictably on USB-3 ports if the hardware and/or software was designed on a USB-2 platform. Granted, USB-3 is supposed to be backward-compatible with USB-2, but USB-2 hardware+software may not be ¡°forward¡±-compliant with a USB-3 port.
Is this a direct connection to the PC, or are you connecting through a USB hub? If connecting through a hub, perhaps try a direct connection.
Just reaching for other possibilities. Good luck.
Ken -- WB?OCV
