Validity
The description below is valid for PCS 7 V7.1 onwards.
In PCS 7 V7.0 and PCS 7 V6.x the DCOM settings remain unchanged after activating the OS Runtime.

Introduction
On the SIMATIC PCS 7 OS server the DCOM permissions required for operating the OPC communication (OPC server and OPC client) are defined automatically via the SIMATIC Security Control application (SSC). The SIMATIC Security Control automatically changes other security settings of the system automatically. These include the configuration of the local Windows firewall and other DCOM permissions required for operating the SIMATIC PCS 7 system.

Depending on the operating mode of the OS server (WinCC - Standard mode (compatibility mode) or WinCC - Service mode), DCOM settings are reset to their original values when the server starts in order to ensure system functionality. These settings include the DCOM setting of the user who executes the OPC server or for whom the authentication for DCOM access is checked.

If a different user was set in the DCOM settings for authentication, this change is reset automatically to the interactive user by the Start scripts of the OS Runtime. The interactive user is the user who executed Windows login and activated the OS Runtime.

Remedy
If the OPC client uses login data (user name, password) for accessing the WinCC OPC server that is different to that used by the OS Runtime, you must proceed according to the system manual "WinCC V7.0 SP1 - Installation / Release Notes" available in Entry ID: 37437018.

The relevant information is in the sections below:

• 3.4.5.1 "Define Access Rights in Operating System" (references to the SIMATIC HMI group)
• 3.4.5.2 "Add Users to the "SIMATIC HMI" User Group"