# Port conflict causing OPC UA failure

**URL:** <https://community.br-automation.com/t/port-conflict-causing-opc-ua-failure/8991>\
**Category:** B&R Software & Runtime\
**Tags:** opc-ua\
**Created:** [November 9, 2025, 5:18pm UTC](https://community.br-automation.com/t/port-conflict-causing-opc-ua-failure/8991 "2025-11-09T17:18:04Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Vojtech\_Jemelka](https://avatars.discourse-cdn.com/v4/letter/v/FF8800/32.png) [@Vojtech\_Jemelka](https://community.br-automation.com/u/Vojtech_Jemelka)\
**Post date:** [November 9, 2025, 5:18pm UTC](https://community.br-automation.com/t/port-conflict-causing-opc-ua-failure/8991/1 "2025-11-09T17:18:04Z")

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Hello,

I have the same trouble. But even when I use your project xxx with the user and role, I got the same message when going to monitor mode. (Connection to OPC UA server not possible.  
(For more details please refer to the help.)) I am desperate. I do not know what to try next.

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**Author:** ![marcel.voigt](https://dub1.discourse-cdn.com/brcommunity/user_avatar/community.br-automation.com/marcel.voigt/32/97_2.png) [@marcel.voigt](https://community.br-automation.com/u/marcel.voigt)\
**Post date:** [November 9, 2025, 9:35pm UTC](https://community.br-automation.com/t/port-conflict-causing-opc-ua-failure/8991/2 "2025-11-09T21:35:10Z")

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I just posted on a different question but sounds like you have a similar issue and the OpcUa server is not enabled.  
Please check

> [@Cant simulate offline](https://community.br-automation.com/t/cant-simulate-offline/8905/7):
>
> Not sure where the help link leads but my guess would be that you need to enable the OpcUa system in the configuration. This help section explains the steps [OpcUa server configuration](https://help.br-automation.com/#/en/6/communication/opcua/configuration/runtime/opcua_runtimeconfiguration.html) or check out this page explaining the required setup for [Ladder monitor mode](https://help.br-automation.com/#/en/6/diagnostics_support/diagnosis/monitormode/diagnosis_monitormode_ladder.html)

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**Author:** ![christoph.hilchenbac](https://dub1.discourse-cdn.com/brcommunity/user_avatar/community.br-automation.com/christoph.hilchenbac/32/423_2.png) [@christoph.hilchenbac](https://community.br-automation.com/u/christoph.hilchenbac)\
**Post date:** [November 10, 2025, 8:01am UTC](https://community.br-automation.com/t/port-conflict-causing-opc-ua-failure/8991/3 "2025-11-10T08:01:19Z")

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Thanks, Marcel,

just want to add this link:

[No OPC UA connection to ARsim](https://help.br-automation.com/#/en/6/visualization%2Fmappview%2Fguides%2Ffaq%2Fruntime_system_faq%2Farsim_opcua.html)

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**Author:** ![Vojtech\_Jemelka](https://avatars.discourse-cdn.com/v4/letter/v/FF8800/32.png) [@Vojtech\_Jemelka](https://community.br-automation.com/u/Vojtech_Jemelka)\
**Post date:** [November 10, 2025, 6:03pm UTC](https://community.br-automation.com/t/port-conflict-causing-opc-ua-failure/8991/4 "2025-11-10T18:03:21Z")

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Hello Christopher,

thanks for this link. The issue was as described in that link - the port 4840 was used by other process. I just changed it to 4841 and it works now.