By 953313493@qq.com , 26 August, 2022 Forums General discussion int CGXDLMSClient::ParseApplicationAssociationResponse( CGXByteBuffer& reply) at last I think should set m_Settings.SetConnected((DLMS_CONNECTION_STATE) (m_Settings.GetConnected() | DLMS_CONNECTION_STATE_DLMS)); befor equals = challenge.Compare(value.byteArr, value.GetSize()); on line 1040 https://github.dev/Gurux/Gurux.DLMS.cpp