WinCC V7.5 Client Graphics Fail After Redundant Server Switchover

Problem Description

On SIMATIC WinCC V7.5 (and higher) runtime systems configured as a redundant server pair (also called WinCC Redundancy or "WinCC/Redundancy" option), the WinCC client stations intermittently fail to load process pictures when the runtime authority switches from the primary server to the redundant partner. The defect is observed on systems updated to WinCC V7.5 Update 19 and later, but the same symptom is reproducible on earlier V7.5 update levels and on WinCC Professional V16+ projects that use the SIMATIC shell configuration layer.

The defect is characterized by the following user-visible behaviour:

• The client picture window shows a permanent hourglass (wait cursor) instead of the configured process graphics.
• Navigation in the configured screen tree (button tree, picture change macros) is blocked.
• The WinCC Explorer on the redundant partner shows the green runtime indicator arrow; the project is reported as "active" with no alarm or error banner.
• The Server Data load on the client completes without a hard error message; pictures simply do not redraw.
• Temporarily deactivating the redundant partner's project restores picture loading on the client. Reactivating the partner reproduces the fault.

Because no fault code or alarm is raised, the issue is frequently misclassified as a server-data corruption problem when the root cause is a client-to-server negotiation failure on the lower RPC/DCOM layer.

Affected Products and Versions

Root Cause Analysis

Two configuration gaps combine to cause the switchover-time picture failure:

1. SIMATIC shell "Remote Communication" not enabled on the redundant servers. Starting with WinCC V7.5 and WinCC Professional V16, the SIMATIC shell (the Settings application launched from the Windows notification area) controls remote access to the WinCC database. When the partner server is brought to "active" runtime, it must publish its server data to the same client; if the publishing endpoint is locked, the client receives an empty/incomplete server-data image and stalls in the picture load.
2. Windows network prerequisites not satisfied. The redundant partner must be reachable by the client over the same NetBIOS / DNS / firewall rules used for the primary server. Microsoft tightened NetBIOS-over-TCP/IP and SMB defaults on Server 2016+, and the SQL Server instance embedded in WinCC also relies on the same network path during switchover.

The two gaps reinforce each other: even with correct network paths, a server that has not enabled Remote Communication will not respond to the client's server-data query; even with Remote Communication enabled, a server that the client cannot resolve by name or reach on the RPC ports will still produce the same hourglass symptom.

Preconditions for the Fault

The fault appears when all of the following conditions are true:

• The WinCC project is configured as a redundant server pair (two servers with matching project ID and matching server data).
• The WinCC client has been loaded with a complete, current server data set from at least one of the servers.
• The redundant server is started, brought to runtime, and at least one switchover has occurred (manual or automatic after failure).
• On the redundant server, the Remote Communication entry in the SIMATIC shell is set to Deactivated.
• Network name resolution (DNS and/or NetBIOS) and firewall rules between the client and the redundant server are not aligned with the requirements documented in Siemens FAQ 868014.

Diagnostic Procedure

Perform the checks in this order. Each step produces a binary pass/fail result; only move to the next step if the current step passes.

1. Confirm the runtime state on the redundant server. Open WinCC Explorer on the redundant server. The status bar at the bottom must show the green arrow and "Server: active". If it shows "Server: inactive" or a yellow triangle, fix the local server problem first; the client-side hourglass is a secondary effect.
2. Check the Windows Event Viewer on the client (Applications and Services Logs → Siemens Automation → License/Trace if present, otherwise Windows Logs → Application and System). Look for DCOM errors with event ID 10010, RPC errors with event ID 1722, or SQL Server named-pipe errors at the time of the switchover.
3. Test name resolution from the client to the redundant server. Open a command prompt and run ping <redundant_server_name> and nslookup <redundant_server_name>. Both must return the same IP address that the server reports in ipconfig /all.
4. Test the SQL Server named-pipe path with Test-NetConnection -ComputerName <redundant_server> -Port 135 (PowerShell) and a follow-up net use \\<redundant_server>\C$ to confirm SMB and RPC reachability.
5. Inspect the SIMATIC shell on the redundant server. Right-click the SIMATIC shell icon in the notification area → Settings → WinCC Explorer tab. The Remote Communication row must read Activated. If it reads Deactivated, the client will be able to load pictures only while the redundant server is not running.

Resolution Path A: Enable Remote Communication in SIMATIC Shell

Applies to WinCC V7.5 and WinCC Professional V16 and higher on both members of the redundant pair.

1. Log on to the redundant server with a Windows account that is a member of the local SIMATIC HMI group.
2. Right-click the SIMATIC shell icon in the system tray and choose Settings... (on Server 2016/2019/2022, the icon may be hidden under the up-arrow in the tray; expand it first).
3. Switch to the WinCC Explorer tab.
4. Click the Remote Communication entry and select Activate from the action list.
5. Confirm the dialog. The entry must read Activated. If the entry is greyed out, the local WinCC project is still running; stop the runtime, repeat the step, then start the runtime again.
6. Repeat steps 1-5 on the primary server so the client gets a consistent server-data image from both partners.
7. On each WinCC client, deactivate the current project, reload the server data from each server in turn (right-click on the server in WinCC Explorer → Server Data → Load), then reactivate the project.

Resolution Path B: Align Windows Network Configuration

Apply the prerequisites in Siemens FAQ "What are the requirements for operating SIMATIC WinCC in a Windows network?". The condensed checklist is reproduced below for field use.

1. DNS host records. Both servers must have a static A record (and, if IPv6 is used, a matching AAAA record) in the same DNS zone the client uses. The client must not rely on NetBIOS-only name resolution; open ncpa.cpl → adapter → Properties → Internet Protocol Version 4 → Advanced → DNS tab and verify that the primary DNS suffix is set and that "Register this connection's addresses in DNS" is enabled.
2. WINS / NetBIOS. If the site uses WINS, add both server entries. If WINS is not used, set NetBIOS over TCP/IP to Enabled or Default on the adapter advanced settings; do not force-disable it on a redundant pair.
3. Firewall rules. On Windows Server 2016+, enable the predefined rules "Windows Management Instrumentation (WMI)", "Remote Service Management", and "File and Printer Sharing (SMB-In)" for the relevant profiles. Additionally, open TCP port 135 (RPC endpoint mapper) and the dynamic RPC range 49152-65535 between the client and both servers. For WinCC specifically, add inbound rules for the WinCC service executables (CCExp.exe, CCProjectMgr.exe, CCAlgRtServer.exe) located in C:\Program Files (x86)\Siemens\Automation\WinCC\bin\.
4. SQL Server access. WinCC uses a SQL Server instance named WinCC. Verify that the SQL Server service is started on both servers and that the SQL Server Browser service is running (it publishes the named-instance port). From the client, run sqlcmd -S <server>\WinCC -E -Q "SELECT @@SERVERNAME" to confirm that Windows authentication reaches the instance.
5. DCOM permissions. The Windows account that runs the WinCC client must be granted the local Remote DCOM Users group membership on both servers, and the account must also be a member of SIMATIC HMI. The DCOM Config → My Computer → Properties → COM Security tab must allow remote access for the relevant accounts.
6. Time synchronisation. The client and both servers must be within 5 minutes of each other (Kerberos tolerance). Use the same NTP source on all three machines.

Resolution Path C: Reload the Server Data on the Client

After enabling Remote Communication and validating the network path, force a clean server-data reload on the affected client:

1. On the client, open WinCC Explorer.
2. Deactivate the project: File → Exit WinCC Explorer (or use the Deactivate button if the project is in runtime).
3. In the navigation tree, right-click Server Data and select Load.... Point the dialog at the redundant server, then repeat the step for the primary server.
4. Confirm that the version number of the loaded server data matches the version published by each server (visible in the server's WinCC Explorer title bar).
5. Reactivate the project and verify that pictures load.

Verification

Perform the following acceptance test on a healthy redundant pair:

1. Start WinCC runtime on both servers. Verify on the client that pictures load and the green connection icon appears for both servers.
2. Trigger a manual switchover from the primary to the redundant partner via WinCC Explorer → Redundancy → Switch Over... on the primary, or stop the WinCC runtime on the primary.
3. On the client, the connection arrow should reorient to the redundant partner within 30-60 seconds. Pictures must redraw within the next picture change; the hourglass must not persist longer than 10 seconds.
4. Force the switchover back to the primary and repeat the check.
5. Open the WinCC diagnostic file <project>_RTLOG.log in C:\Program Files (x86)\Siemens\Automation\WinCC\diagnose\ on the client and confirm no RPC_E_DISCONNECTED, 0x800706BA, or SQL Server does not exist or access denied entries appear at the switchover timestamp.

Extended Troubleshooting Matrix

Preventive Configuration

To avoid the fault recurring after a future change, codify the following configuration in the plant standards document:

• Both redundant servers and all clients must join the same Active Directory domain and use DNS for name resolution. WINS is permitted as a fallback, not as the primary mechanism.
• The Remote Communication entry in the SIMATIC shell must be Activated on every WinCC server. The activation step must be included in the system acceptance test (FAT/SAT) checklist.
• A scheduled PowerShell script must check the registry value HKLM\SOFTWARE\Wow6432Node\Siemens\Automation\WinCC\RemoteComm\Active on each server monthly; the value must be 1.
• Firewall rule sets for WinCC must be exported and stored in the network management system so that any change to a server's profile is documented and revertable.
• The redundant pair must run the same WinCC update level and the same Windows cumulative update level; drift between the two is a frequent cause of switchover asymmetry.

Common Field Pitfalls

• Stop the runtime first. Remote Communication cannot be toggled while WinCC runtime is running. Operators sometimes complain that the setting "won't stick" because the runtime is rewriting the registry on every start.
• Do not skip the server-data reload. Even after enabling Remote Communication, the client retains the previous server-data snapshot. Without a reload, the client will still attempt to reach the old endpoint and the hourglass will persist.
• Check both directions of the firewall. The client initiates the connection, but the redundant server replies on the dynamic RPC range. A firewall on the client (not the server) is sometimes the culprit.
• Time skew breaks Kerberos. A 6-minute clock drift between the client and the server silently fails authentication; the connection arrow turns yellow, not red, and is easy to miss.

Related Siemens Documentation

• Siemens FAQ 868014 – Requirements for operating SIMATIC WinCC in a Windows network
• Siemens FAQ 109769234 – Activating "Remote Communication" in the SIMATIC shell for WinCC V7.5 and higher
• SIMATIC WinCC V7.5 system manual, sections on Redundancy and Client/Server configuration

Frequently Asked Questions