Resolving WinCC Error While Requesting the Interface for the Data Storage in Server-Client Architectures

The WinCC error 'Error while requesting the interface for the data storage' occurs when an OS Client attempts to open a remote server project (*.mcp) but cannot establish DCOM, RPC, or SQL communication over the Terminal Bus. The root causes are misconfigured SIMATIC Shell network adapter bindings, conflicting virtual network cards, Windows Network Profiles set to Public rather than Private/Domain, or disabled remote communication settings. Resolving it requires selecting the active Terminal Bus adapter in SIMATIC Shell, removing ghost network adapters, and enabling remote communication across all nodes.

Root Causes of Terminal Bus Data Storage Interface Failures

In SIMATIC WinCC V7.5 / PCS 7 client-server architectures, thin clients access server project metadata via Microsoft Component Object Model (COM/DCOM) and SQL Server native interfaces. When opening a remote project over a UNC path (e.g., \\Server01\ProjectShare\Project.mcp), WinCC invokes internal storage handlers to query the project's configuration database (*.mdf).

If this fails with the error dialog Error while requesting the interface for the data storage, the root causes include:
1. SIMATIC Shell Network Binding Misconfiguration: SIMATIC Shell is the Siemens broadcast discovery service that coordinates inter-station communication. If SIMATIC Shell is bound to the wrong network card (e.g., a secondary management port, a wireless card, or a virtual hypervisor adapter), the client cannot resolve the server's broadcast announcements.
2. Ghost or Multiple Network Adapters: In virtualized environments (VMware Workstation, ESXi, Hyper-V), secondary host-only or NAT network adapters confuse the Windows network routing table. SIMATIC Shell requires the Terminal Bus adapter to have strict priority.
3. Windows Network Location Set to 'Public': Windows Defender Firewall applies aggressive blocking rules to networks categorized as "Public Network". Port 135 (RPC End Point Mapper), DCOM ports, and SQL Server port 1433 are blocked, preventing interface instantiation.
4. Disabled Remote Communication in SIMATIC Shell: Starting with modern WinCC versions, SIMATIC Shell includes explicit settings to allow or deny remote communication and manage encrypted Terminal Bus security keys.

Step-by-Step Diagnostic and Resolution Procedure

Follow this procedure on both the OS Server and all OS Clients to eliminate the error.

Prerequisites

Direct IP connectivity verified via bidirectional ping (using both IP address and computer hostnames).
Same Windows user account and password belonging to the local SIMATIC HMI group on all machines.
Administrative elevation to modify network adapters and SIMATIC Shell properties.

Step 1: Remove Redundant and Ghost Network Adapters

Open Windows Network Connections (ncpa.cpl).
Identify all network interfaces. In virtual machines, disable or remove unused adapters (such as VMware Host-Only adapters, secondary NAT cards, or VPN tunnels).
Ensure each machine has only two active physical/virtual industrial adapters:
* Terminal Bus: Communication between Clients, OS Servers, and Engineering Stations.
* Plant Bus: Communication between OS Servers and Automation Stations (CP 1623 / Industrial Ethernet).

Step 2: Configure SIMATIC Shell on Server and Client

In Windows File Explorer, navigate to This PC.
Locate SIMATIC Shell in the navigation tree or double-click SIMATIC Shell in the explorer folder view.
Right-click SIMATIC Shell and select Settings....
In the configuration dialog:
* Network Adapter: Explicitly select the network interface assigned to the Terminal Bus (do not leave on default or auto-detect).
* Remote Communication: Ensure the checkbox for Remote communication is enabled.
* Encrypted Communication: If encryption is enabled, verify that both the Server and Client use the identical PSK (Pre-Shared Key). If migrating or testing, disable encryption temporarily on both nodes.
Click OK. SIMATIC Shell will prompt to restart its service.

Step 3: Verify Network Profile and Firewall Settings

Open Windows PowerShell as Administrator.
Run Get-NetConnectionProfile to inspect network category status.
If the Terminal Bus network is set to Public, execute:
Set-NetConnectionProfile -InterfaceAlias "Terminal Bus" -NetworkCategory Private
Confirm that Windows Firewall allows inbound connections for SimaticShell.exe, CCClient.exe, and Microsoft SQL Server.

Step 4: Verify Multi-Node Discovery in SIMATIC Shell

Open SIMATIC Shell on the client PC.
Verify that all participating stations (OS Server 1, OS Server 2, ES) appear in the SIMATIC Shell node list.
If servers appear, right-click the server and confirm project visibility.
Open the project from the client: WinCC Explorer -> File -> Open -> \\Server\Share\Project.mcp.

Verification

In SIMATIC Shell, verify that double-clicking the remote server expands the active project without authorization warnings.
From WinCC Explorer on the client, open the server project. The project database opens smoothly, displaying the Tag Management and Graphics Designer hierarchy without error dialogs.
Activate Runtime on the client: confirm that process screens load and dynamic tag communication establishes immediately.

Limitations and Operational Precautions

Network Card Order and Metric: Ensure the Terminal Bus adapter has metric priority in Windows Advanced TCP/IP settings if multiple network cards reside on the same station.
Avoid Multi-Homed Network Bridging: Never bridge the Terminal Bus and Plant Bus network cards in Windows; bridging introduces security risks and corrupts SIMATIC Shell packet routing.
Workgroup Name Consistency: In workgroup architectures without Active Directory, all machines must share the exact same Windows Workgroup name (e.g., WORKGROUP).

Engineer FAQ

What is the function of SIMATIC Shell?
SIMATIC Shell is a proprietary Siemens network service that uses broadcast/multicast packets to discover PCS 7 and WinCC nodes across the Terminal Bus and manage inter-station security.
Why did ping work even though WinCC failed?
Ping verifies basic ICMP IP routing, but WinCC requires DCOM, RPC endpoint binding, NetBIOS name resolution, and SQL Server authentication across multiple ports.
Does SIMATIC Shell support communication across subnets?
Yes. If clients and servers reside on different subnets, configure the Multicast Proxy or broadcast forwarding IP address within SIMATIC Shell settings.
What ports must be open between WinCC clients and servers?
TCP port 135 (RPC), dynamic RPC ports (1024-65535 or configured range), TCP port 1433/1434 (SQL Server), and SIMATIC Shell broadcast ports.
Can a client open a project if the server project is not shared?
No. The server project folder must be shared with Windows Share permissions and NTFS security granted to the local SIMATIC HMI group.

Technical References

Siemens Industry Online Support Entry ID 109769234: SIMATIC Shell Configuration Guidelines for WinCC Client-Server Systems.
Siemens WinCC V7.5 SP2 System Manual: Configurations and Server-Client Architecture.
Microsoft Support Document: DCOM and RPC Configuration for Distributed Applications.

Resolving WinCC Error While Requesting the Interface for the Data Storage in Server-Client Architectures