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OPCUA: Unexpected error. Retrieved namespace list contain no entries

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19 Sep 2026 17:36 - 19 Sep 2026 17:37 #14695 by support
Replied by support on topic OPCUA: Unexpected error. Retrieved namespace list contain no entries
Hello. The short answer is "preferably and most likely not", but I think you deserve longer explanation, in order to understand the reasons behind. First, let me state that when we develop our own code for OPC client side, we have a rule that we obey quite consistently, and that is "the software should be forgiving to incompliant or incorrect behavior of the OPC server to the maximum extent possible, except when there is a security concern". We actually go to great lengths, and spend considerable effort to overcome such behaviors of many OPC servers, whenever we encounter them in testing. We want that our customers take our software and experience that "it just works". This said, the important part in the above statement is "our own code". QuickOPC relies on OPC UA .NET stack and (part of) SDK for the low-level OPC UA communication parts. And, if nothing else than for security reasons, we need to take newer versions of these libraries, when they are available. I understand that the issue you are dealing with is perceived as a regression in behavior, because it worked for you in earlier QuickOPC version. But there was no change in "our code" related to it. It appeared strictly because new checks have been introduced into OPC UA .NET stack & SDK, and we have taken over a newer version of these libraries. Moreover, these checks are not incorrect - they assume compliant OPC server - it's just that these libraries do not quite follow the same "forgiving" philosophy as we do (or at least not consistently). So now to the actual list of reasons: 
  1. "Not our code", as explained above. In order to work around the issue, we would have to basically fork and modify the UA .NET stack & SDK, and maintain a forked version from this point onwards. That is quite a hassle, and carries relatively high, real costs with it.
  2. Most OPC servers we deal with are not certified, but do not have any serious issues (or only have the issues we have already taken care of). Let's call them Level 2. Let's call certified server level 3 - they are much better. Then, from time we encounter a server with a serious issue, a "substandard" server - let's call these server Level 1, and we try to work around the issue. But, I have never encountered a piece of software (it is hard to call it OPC UA server) like the one you are dealing with. It would be something like Level 0, or Level -1. It look like that somebody just had hooked together pieces of code handling the very basics of OPC UA protocol, without realizing that OPC UA is not just about message exchange. Even with our "forgiving" philosophy, we have not intended to support such really bad software.
  3. Developing the workaround would be difficult because we are missing a server (or access to server endpoint) to test with.
  4. The error you are getting now has to do with missing NamespaceTable in the server. Suppose that we develop a workaround for it. The error will be gone, but there is nothing that guarantees that other stuff will work. You may get a different error then, because there may be more checks inside the UA .NET stack & SDK. It is not quite possible to tell upfront whether something else will have to be changed (worked around) too, how much of it will be needed, and whether it will be realistically possible. 
Best regards
 
Last edit: 19 Sep 2026 17:37 by support.

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17 Sep 2026 13:32 #14694 by Andriy
Replied by Andriy on topic OPCUA: Unexpected error. Retrieved namespace list contain no entries
Hello,
Is it possible to find/implement a workaround for non-compliant OPCUA servers that do not expose mandatory OPCUA address space nodes?

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14 Sep 2026 11:24 #14693 by support
Replied by support on topic OPCUA: Unexpected error. Retrieved namespace list contain no entries
Hello,

what you are dealing with is not a compliant OPC UA server. From the address space picture you sent, it is missing the whole Server object, an many other things. It can hardly be called OPC UA server at all.

The fact that older QuickOPC version could connect, or that UaExpert can connect, does not invalidate this conclusion.

Not a bug on our side.

Regards
 

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14 Sep 2026 10:47 #14692 by Andriy
Replied by Andriy on topic OPCUA: Unexpected error. Retrieved namespace list contain no entries
Hello,1. We don't have evidence that the issue is related to server certificate, most likely it's not
2. The customer did not disclose that information, its likely the server resides on PLC
3. The customer did not disclose that information
4. Multiple clients are able to establish connection to the server: UA Expert 1.6, UA Expert 2.0.0, client based on OpcLabs QuickOPC v.5.83.477 (same source code).
5. The issue is reproducible with all 3 communication modes: None, Sign, SignAndEnctypt with exactly the same error
6. The issue happens always Additional information:
  • the server has limited protocol support: subscription not supported, probably other limitations 
e.g UA Expert 1.6 client shows the following warnings and errors:
Warning. General: Browsing binary DataTypeSystem failed - no dictionaries found.
Error. AddressSpaceModel: Register for ModelChangeEvents failed: createSubscription returned BadServiceUnsupported
- None of the above prevent UA Expert to browse items and read item attributes including value
  • QuickOPC v.5.83.477 is also able to establish connection and poll item value with ReadMultiple method
 
  • uaexpert.png

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    12 Sep 2026 09:18 #14691 by support
    Replied by support on topic OPCUA: Unexpected error. Retrieved namespace list contain no entries
    Hello.

    1) I do not see why this issue should be related to  forum.opclabs.com/forum/quickopc-net/4645-opcua-acceptanycer...s-not-work-in-v-5-84-192#14688 except for the fact that it might happen with the same server. Please explain why you think so.
    2) Do you know which server it is? (vendor, model, version)?
    3) Is the server certified for OPC UA compliance?
    4) Are the other OPC UA clients connecting to that server? What clients are they? With what results?
    5) What is the message communication mode you use? None, Sign, or SignAndEncrypt? 
    6) Does this error happen always (i.e. you are unable to ever connect to the server with QuickOPC), or only sometimes?

    Regards
     

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    11 Sep 2026 12:39 #14690 by Andriy
    OPCUA: Unexpected error. Retrieved namespace list contain no entries was created by Andriy
    Hello,
    We are experiencing the issue with "OpcLabs.QuickOpc" Version="5.84.374". It works fine with the same source code and configuration in v "5.83.477"
    The issue reproduces on the customer's opcua server which we do not have access to. Let me know what additional information/logs you need to investigate the issue
    it is related to the ticket  OPCUA: AcceptAnyCertificate does not work in v.5.84.192
    Code:
    [13:44:34 ERR] OnServerConditionChanged: endpoint opc.tcp://xxx:4840 changed to Disconnected. Error: OpcLabs.UAEngine=1 UA SDK error (Opc.UA.ServiceResult=0x80010000) in 'static Session.Create'. OPC UA service result - {BadUnexpectedError}. Retrieved namespace list contain no entries. Retrieved namespace list contain no entries. + Connection attempt #1; last connected at 1/1/0001 12:00:00 AM (local); unconnected for 00:00:00.0310000. + The client method called (or event/callback invoked) was 'ServerConditionChanged'. OpcLabs.EasyOpc.UA.Engine.UAEngineException: UA SDK error (Opc.UA.ServiceResult=0x80010000) in 'static Session.Create'. OPC UA service result - {BadUnexpectedError}. Retrieved namespace list contain no entries. Retrieved namespace list contain no entries. + Connection attempt #1; last connected at 1/1/0001 12:00:00 AM (local); unconnected for 00:00:00.0310000. + The client method called (or event/callback invoked) was 'ServerConditionChanged'. ---> OpcLabs.EasyOpc.UA.UAServiceException: OPC UA service result - {BadUnexpectedError}. Retrieved namespace list contain no entries. Retrieved namespace list contain no entries.    at Opc.Ua.Client.Session.UpdateNamespaceTable(DataValueCollection values, DiagnosticInfoCollection diagnosticInfos, ResponseHeader responseHeader)    at Opc.Ua.Client.Session.FetchNamespaceTablesAsync(CancellationToken ct)    --- End of inner exception stack trace --- == Activity Trace == Following (15) events were gathered during the action on activity ID [15], in the order of first occurrence:   SDK trace: 09/11/2026 13:44:33.997 Imported the PFX private key for zzz (with Private Key).   2*[44] Exception: {Opc.Ua.ServiceResultException} [801A0000] 'Certificate is not trusted.'   [44] SDK trace: 09/11/2026 13:44:34.204 Validation errors suppressed: zzz   2*Exception: {Opc.Ua.ServiceResultException} [801A0000] 'Certificate is not trusted.'   SDK trace: 09/11/2026 13:44:34.252 Validation errors suppressed: zzz   [43] Exception: {Opc.Ua.ServiceResultException} Retrieved namespace list contain no entries.   5*Exception: {System.AggregateException} One or more errors occurred.   2*Exception: {Opc.Ua.ServiceResultException} Channel has been closed. Events starting with activity ID in may not necessarily be related to the current action. PollItems: endpoint opc.tcp://xxx:4840, item ns=1;s=PFC200_WAGO_OPC_SL01 failed. Error: OpcLabs.UAEngine=1 UA SDK error (Opc.UA.ServiceResult=0x80010000) in 'static Session.Create'. OPC UA service result - {BadUnexpectedError}. Retrieved namespace list contain no entries. Retrieved namespace list contain no entries. + Connection attempt #1; last connected at 1/1/0001 12:00:00 AM (local); unconnected for 00:00:00.0310000. + The client method called (or event/callback invoked) was 'ServerConditionChanged'. OpcLabs.EasyOpc.UA.Engine.UAEngineException: UA SDK error (Opc.UA.ServiceResult=0x80010000) in 'static Session.Create'. OPC UA service result - {BadUnexpectedError}. Retrieved namespace list contain no entries. Retrieved namespace list contain no entries. + Connection attempt #1; last connected at 1/1/0001 12:00:00 AM (local); unconnected for 00:00:00.0310000. + The client method called (or event/callback invoked) was 'ServerConditionChanged'. ---> OpcLabs.EasyOpc.UA.UAServiceException: OPC UA service result - {BadUnexpectedError}. Retrieved namespace list contain no entries. Retrieved namespace list contain no entries.    at Opc.Ua.Client.Session.UpdateNamespaceTable(DataValueCollection values, DiagnosticInfoCollection diagnosticInfos, ResponseHeader responseHeader)    at Opc.Ua.Client.Session.FetchNamespaceTablesAsync(CancellationToken ct)    --- End of inner exception stack trace ---

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