# Bug: RW 7.15.2 OPC U/A Subscribe issue on embedded OPC server

**URL:** <https://tech-community.robotics.abb.com/t/bug-rw-7-15-2-opc-u-a-subscribe-issue-on-embedded-opc-server/11634>\
**Category:** OmniCore\
**Created:** [September 30, 2024, 9:03am UTC](https://tech-community.robotics.abb.com/t/bug-rw-7-15-2-opc-u-a-subscribe-issue-on-embedded-opc-server/11634 "2024-09-30T09:03:48Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Fanny](https://avatars.discourse-cdn.com/v4/letter/f/b38774/32.png) [@Fanny](https://tech-community.robotics.abb.com/u/Fanny)\
**Post date:** [September 30, 2024, 9:03am UTC](https://tech-community.robotics.abb.com/t/bug-rw-7-15-2-opc-u-a-subscribe-issue-on-embedded-opc-server/11634/1 "2024-09-30T09:03:48Z")

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Hello!  
Im trying to setup OPC client with a subscription on OPC variables on a irb6730 Rw 7.15.2 directly to the OPC U/A server on the controller, hence not through IoT Gateway, and it keeps giving me null reference exception.

It works to read and write the variables directly, but when I try to setup the subscription, I provide the variable paths for existing variables and a callback to handle when the variables has changed, I keep getting the following exception:

System.NullReferenceException  
HResult=0x80004003  
Message=Object reference not set to an instance of an object.  
Source=Opc.UaFx.Advanced  
StackTrace:  
at Opc.Ua.Client.Session.ProcessPublishResponse(ResponseHeader responseHeader, UInt32 subscriptionId, UInt32Collection availableSequenceNumbers, Boolean moreNotifications, NotificationMessage notificationMessage)

When I do exactly the same thing through IoTGateway, I manage to subscribe without no issue and exception?  
I would really like to use the embedded server and not IoT gateway since this requires the standalone application to run on a computer.

I have tried this on RW 7.15.2 with irb6730 and also tried it with gofa (some earlier RW), same issues..

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**Author:** ![Maxim](https://dub1.discourse-cdn.com/flex005/user_avatar/tech-community.robotics.abb.com/maxim/32/4429_2.png) [@Maxim](https://tech-community.robotics.abb.com/u/Maxim)\
**Post date:** [September 30, 2024, 9:05am UTC](https://tech-community.robotics.abb.com/t/bug-rw-7-15-2-opc-u-a-subscribe-issue-on-embedded-opc-server/11634/2 "2024-09-30T09:05:54Z")

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Hello @Fanny,

Please reach out to your local ABB and report this issue as a potential bug.  
[https://new.abb.com/contact-centers](https://new.abb.com/contact-centers)

Thanks!

Best regards,  
Maxim

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<div class="post-metadata">

**Author:** ![Fanny](https://avatars.discourse-cdn.com/v4/letter/f/b38774/32.png) [@Fanny](https://tech-community.robotics.abb.com/u/Fanny)\
**Post date:** [September 30, 2024, 9:25am UTC](https://tech-community.robotics.abb.com/t/bug-rw-7-15-2-opc-u-a-subscribe-issue-on-embedded-opc-server/11634/3 "2024-09-30T09:25:53Z")

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@Maxim thank you! I have contacted them now.

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**Author:** ![Fanny](https://avatars.discourse-cdn.com/v4/letter/f/b38774/32.png) [@Fanny](https://tech-community.robotics.abb.com/u/Fanny)\
**Post date:** [October 1, 2024, 2:00pm UTC](https://tech-community.robotics.abb.com/t/bug-rw-7-15-2-opc-u-a-subscribe-issue-on-embedded-opc-server/11634/4 "2024-10-01T14:00:00Z")

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The answer from Robot support is that the subscribe functionality is not available right now in the embedded server. The planned release is RW 7.17, and it requires the option 3154-2 IoT Data Client.