# Modbus USB PORTNOTOPENERROR
**URL:** https://discourse.nodered.org/t/modbus-usb-portnotopenerror/36324
**Category:** General
**Created:** [22 November 2020 11:34 UTC](https://discourse.nodered.org/t/modbus-usb-portnotopenerror/36324 "2020-11-22T11:34:43Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@bert2713d](https://discourse.nodered.org/u/bert2713d)
#### Post date: [22 November 2020 11:34 UTC](https://discourse.nodered.org/t/modbus-usb-portnotopenerror/36324/1 "2020-11-22T11:34:43Z")
dear All
I using node-red to convert a Modbus signal to MQTT .
It was working fine. However I have install on my raspberry Pi4 a SSH and VNC connection in order to have a distance access. I do not know if it is linking but now , node-red said me that :
"Error: {"name":"PortNotOpenError","message":"Port Not Open","errno":"ECONNREFUSED"}"
I am using the " /dev/ttyUSB0" designation .
I have seach hours on forum and internet but didn't find an easy answer about this permission needed.
could you help ?
regards
Beber
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### Author:  [@JohnBreslin](https://discourse.nodered.org/u/JohnBreslin)
#### Post date: [24 November 2020 14:25 UTC](https://discourse.nodered.org/t/modbus-usb-portnotopenerror/36324/2 "2020-11-24T14:25:45Z")
Hi Bert,
I am experiencing the same issue on a Raspberry Pi4 but it works fine under Windows10. Did you get any other feedback?
regards,
JohnB
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### Author:  [@system](https://discourse.nodered.org/u/system)
#### Post date: [23 January 2021 14:25 UTC](https://discourse.nodered.org/t/modbus-usb-portnotopenerror/36324/3 "2021-01-23T14:25:53Z")
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