Hi,

My advice is to stop using a “legacy stack”, which is pretty much discontinued completely by the OPC Foundation at this point and use a proper SDK-level library/framework for your OPC UA needs. The readme in https://github.com/OPCFoundation/UA-AnsiC-Legacy says “This repository (https://github.com/OPCFoundation/UA-AnsiC-Legacy) will be closed end of February 2021.”

Generally speaking, you are completely on your own if you use a bare “stack” level implementation. Using those requires expertise in OPC UA and even with that they usually simply lack features to deal with the every growing feature set which OPC Foundation is continously increasing.

That being said, the error code in the full form is Bad_SessionClosed, 0x80260000, “The session was closed by the client.”. You can check if the simulation server logs indicate anything, they are written by default /.prosysopc/prosys-opc-ua-simulation-server/log/.

Do you mean by “activate session”, that you made both CreateSession and ActivateSession calls with both succeeding, and you are using the authentication token returned in CreateSessionResponse in the ActivateSession and all further calls? Failing to do these would be one cause, which would been seen by the client by that error code. Typically all that is implemented by an SDK-level framework internally.