Diagnosing Intermittent Server License Warnings and Network Disconnections on WinCC OS Clients

On SIMATIC PCS 7 WinCC OS Clients, intermittent warnings stating 'Server License Problem' or missing license keys—occurring when other clients and the OS Server operate normally—are caused by transient Terminal Bus network interruptions, energy-saving network card power states, or blocked DCOM/RPC communication between the client and the Automation License Manager (ALM) on the OS Server. To resolve this, disable power-saving features ('Energy Efficient Ethernet') on the client network adapter, configure persistent static IP/hostname mappings in the Windows 'hosts' and 'lmhosts' files, and ensure 'Allow remote connections' is checked in ALM on the OS Server.

Executive Summary

In SIMATIC PCS 7 distributed control systems, Operator Stations operate in a client-server architecture where OS Clients rely on OS Servers for process tags, historical alarms, and license validation. Occasionally, plant personnel observe an alarming symptom: a single OS Client displays intermittent error pop-ups such as Server License Problem or Missing License Key, even though the client possesses valid local licenses and all other OS Clients and Servers continue operating without issue.

Because OS Clients do not store server runtime licenses locally, engineers frequently misdiagnose this error as a licensing shortage or corrupted license key in Automation License Manager (ALM). In reality, this popup is almost always triggered by underlying communication degradation: if the client briefly loses socket connectivity, experiences high packet loss, or fails RPC name resolution to the OS Server, the client's WinCC runtime engine assumes the server license has expired. This guide provides the diagnostic methodology to identify network dropouts and eliminate intermittent server license warnings.

Architecture and Fundamental Mechanics

The client-server licensing and communication architecture in WinCC relies on synchronized RPC and DCOM sessions:

Client-Server License Validation Architecture:
- WinCC OS Clients require a local WinCC OS Client runtime license.
- Technological Process Objects (POs) and server runtime capabilities are licensed exclusively on the OS Server.
- During runtime, the OS Client maintains continuous background Remote Procedure Call (RPC) and DCOM polling sessions with the OS Server to validate server package access and verify licensing.
The False License Error Phenomenon:
- When an OS Client experiences a transient network drop (e.g., spanning 2 to 5 seconds):
- WinCC Data Manager (CCDataMgr.exe) fails to refresh its server heartbeat.
- The local licensing client queries ALM on the remote server over TCP port 4410.
- Because the network link is temporarily unresponsive, the query times out.
- WinCC interprets the absence of server confirmation as a licensing defect, generating the misleading pop-up: Server License Problem.
Common Root Causes of Transient Disconnections:
- Network Adapter Power Management: Windows 10/Server power-saving features (such as 'Green Ethernet', 'Energy Efficient Ethernet', or 'Allow the computer to turn off this device to save power') temporarily throttle the network interface controller (NIC) during idle periods.
- Hostname Resolution Failures: If DNS or NetBIOS name resolution experiences intermittent delays, RPC calls stall.
- Subnet Routing and Managed Switch Configuration: Port duplex mismatches (e.g., Auto-negotiate vs 100/1000 Full) or spanning-tree topology recalibrations cause intermittent packet drops.

Step-by-Step Implementation Procedure

Follow these steps to diagnose and eliminate intermittent server license warnings on OS Clients:

Disable Network Adapter Power Saving Features:
- On the affected OS Client, press Win + R, type ncpa.cpl, and press Enter.
- Right-click the Terminal Bus network adapter and select 'Properties'.
- Click 'Configure...' and switch to the 'Power Management' tab.
- UNCHECK 'Allow the computer to turn off this device to save power'.
- Switch to the 'Advanced' tab:
- Set 'Energy Efficient Ethernet' to 'Disabled'.
- Set 'Green Ethernet' to 'Disabled'.
- Ensure 'Speed & Duplex' is set to match the switch port (typically '1.0 Gbps Full Duplex' or 'Auto Negotiation').
- Click 'OK' to apply changes.
Configure Static Host Name Resolution (hosts and lmhosts):
- Open Windows Notepad as Administrator.
- Open C:\Windows\System32\drivers\etc\hosts.
- Add static IP-to-hostname entries for all OS Servers, redundant partners, and the Engineering Station:
text 192.168.1.10 OS_SERVER_A # Primary OS Server 192.168.1.11 OS_SERVER_B # Redundant OS Server
- Open C:\Windows\System32\drivers\etc\lmhosts.sam.
- Add corresponding entries with the #PRE tag to preload names into the NetBIOS cache.
- Save the file as lmhosts (without extension).
Verify ALM Remote Connection Settings on OS Server:
- On the OS Server, open Automation License Manager (ALM).
- Select 'File > Settings...' > switch to the 'Connection' tab.
- Verify that 'Allow remote connections' is checked.
- Verify that 'Allow remote license key operation' is checked.
- Confirm that TCP port 4410 is open in Windows Firewall.
Inspect WinCC Diagnostic Logs:
- On the client PC, navigate to C:\Program Files (x86)\Siemens\WinCC\diagnose\.
- Open WinCC_Sys_01.log and SIMATIC_S7_PROTOCOL_SUITE.LOG.
- Search for timestamps matching the license popup: confirm the presence of communication errors such as Connection broken, RPC timeout, or Cannot connect to server.
Test Continuous Ping Stability:
- Open Command Prompt on the client PC and execute a continuous ping to the OS Server:
ping -t 192.168.1.10
- Let it run for several hours to detect intermittent packet drops or latency spikes exceeding 100 ms.

Verification

Run WinCC Runtime on the OS Client under normal plant operating conditions.
Verify that no 'Server License Problem' pop-ups appear during extended shifts.
Open Automation License Manager on the OS Client: connect to the OS Server in the network tree and confirm that server licenses are visible and report status 'In use'.
Review WinCC_Sys_01.log: confirm that heartbeat and DCOM communication logs remain clear of timeout warnings.

Limitations and Operational Precautions

Ensure that the OS Client does not have an incorrect station configuration in SIMATIC Manager (e.g., being inadvertently configured as a Single-Station OS instead of a WinCC Client Application), which would cause it to demand local server licenses. Verify that all OS Clients and Servers share synchronized system time and consistent Windows user credentials. Genuine license procurement and PO capacity expansions should be verified through an authorized Siemens distributor or the Siemens Industry Mall.

Engineer FAQ

Why does a network drop cause a 'Server License Problem' error?

Because the client queries the OS Server across the network to validate runtime server rights. If communication fails, the client software assumes the server license is missing.

Where are WinCC client diagnostic logs stored?

In C:\Program Files (x86)\Siemens\WinCC\diagnose\ (specifically WinCC_Sys_01.log).

What port does Automation License Manager use for remote queries?

ALM communicates across the network using TCP port 4410.

Does an OS Client require its own Process Object (PO) licenses?

No. WinCC OS RT PO licenses are booked and managed exclusively on the OS Server; clients require only a standard WinCC OS Client runtime license.

Why is disabling Energy Efficient Ethernet important?

Energy Efficient Ethernet throttles or suspends network interfaces during low traffic, causing transient connection drops that trigger false license warnings.