Hello,

The OPC UA Specification defines the following use case for StatusCode Bad_CommunicationError:

For Subscriptions that contain Conditions for which the failure applies, the effected Conditions generate an Event, if the Retain field is set to True. These Events shall have their Event fields that are associated with the communication failure contain a StatusCode of Bad_CommunicationError for the value. (https://reference.opcfoundation.org/Core/Part9/v104/docs/5.15)

That is the only defined use case for Bad_CommunicationError in the “core” OPC UA specification. Companion Specifications might define additional use cases.

The general definition for StatusCode Bad_CommunicationError is: “A low level communication error occurred” (https://reference.opcfoundation.org/Core/Part4/v104/docs/7.34.2). The specification does not define more specifically in which situations this StatusCode should be used. In the case of Prosys OPC UA SDK for JAVA, the StatusCode is used parsing a ByteString from the received chunk fails or when all SecurityTokens of a SecureChannel have expired for example. Server applications developed by other manufacturers could be using this StatusCode in different situations.

Therefore, Bad_CommunicationError does not have a well defined meaning and it is practically impossible to tell the exact error based solely on it.

Do you have any additional information on the error such as logs from the Client or the Server? Or a Wireshark capture of messages exchanged between the applications? If you do, you can send those to uajava-support at prosysopc.com so that we can take a look them.

Since you mentioned that you’re trying to subscribe to data from a PLC via a 3rd party OPC UA Server, it could be possible that this StatusCode is used to indicate that there is some communication error between that Server and the PLC, but this is purely a speculation and the real error could be something else. Though, I would recommend you to also contact the manufacturer of the 3rd party Server about this error as well.