Resolving WinCC Unified PC RT License Error During Simulation

Problem Overview

When an engineer launches the WinCC Unified PC RT simulation from TIA Portal V17, V18, V19, V20, or V21, the runtime frequently raises an alarm stating that no valid Unified RT license is available on the engineering station. The alarm appears immediately after the operator clicks Start RT in the project tree, and in a substantial number of first-run cases the simulated project appears to fail to load or freezes on the start screen. The behavior is confusing because the project has not yet been deployed to a real Unified Panel or IPC; the engineer is merely exercising the project in the local simulator.

The alarm is not a hard fault. It is the documented behavior of the Automation License Manager (ALM) hookup that the Unified runtime performs at startup. The official TIA Portal help for V20 and V21 states verbatim under the topic Simulating a project (RT Unified):

If no license is found for Runtime, an alarm appears and the simulation runs in demo mode. After 1 hour, you will be reminded that no license was found.

The same licensing logic is in force in V17 and is documented on page 29 of the SIMATIC WinCC Unified V17 ES & RT Installation Notes: an RT Unified license is required to operate the Unified PC RT, including the simulator that wraps it. Engineers who do not yet hold a Unified RT license key should therefore expect the alarm on every simulation start and should not interpret the alarm as a configuration error.

Root Cause: ALM Hookup at Simulation Start

The Unified PC RT simulator is not a separate engine. It is the real PC runtime launched with a special command-line switch that tells the loader to bind the compiled project to localhost instead of an external HMI device. The full startup sequence executed when the user selects Start RT in TIA Portal is:

1. TIA Portal serializes the active Unified project from the engineering database and writes a temporary .bin runtime container to %ProgramData%\Siemens\Automation\WinCCUnified\RT\<projectname>\.
2. The runtime loader is invoked with the path to the container and the --simulate flag.
3. The loader binds the ES↔RT communication channel. By default the channel is a TCP listener on 127.0.0.1:20008 for the engineering station to query runtime diagnostics.
4. The loader queries the Automation License Manager service (almsrv.exe) for a WinCC Unified PC RT license fingerprint that matches the local hardware.
5. If the ALM returns a valid key, the runtime starts in fully licensed mode. If the ALM returns no key, the runtime starts in demo mode and posts the license alarm to the runtime control diagnostic view.
6. Runtime services (UMC, RT_Station, HmiRTm) are started and the project becomes operable.

Step 4 is the root cause of the alarm. The Unified runtime loader uses the same license validation code path for the simulator and for the production PC runtime, because the simulator is the production runtime. The license check has no awareness that the user is running in offline mode.

Unified PC RT Licensing Model

WinCC Unified ships with two distinct runtime families. Each has its own license catalog in the ALM. Mistaking one for the other is the most common cause of the "license not found" alarm.

Demo Mode and the 1-Hour Timer

When the ALM returns a "no key" response, the runtime does not stop. It switches to demo mode. The user-visible effects of demo mode are:

• The license alarm is written to the runtime control log and is shown in the HMI runtime header bar.
• The runtime remains fully operable. Tags, screens, scripts, logging, and alarms all function as in licensed mode.
• After 3600 seconds (1 hour) of cumulative runtime, the runtime posts a second alarm reminding the operator that no license was found. This reminder is re-issued every 60 minutes until the runtime is restarted with a valid key.
• There is no built-in runtime cap. The demo mode does not expire; it only reminds.

The 1-hour timer is documented in the V20/V21 help text quoted above. It is also the timer enforced by the HmiRTm service when running under a count-limited license (for example, a 256-tag license running a 1000-tag project). In that case, the reminder identifies the missing tag count rather than the missing license class.

Why the Project May Appear Not to Start

Two distinct situations are reported in the field. They have different root causes and different remedies.

Case A: Alarm Posted, Runtime Continues in Demo Mode

The license alarm appears in the runtime header, the start screen resolves, and the project is operable after a delay of 2–5 seconds. This is the expected behavior. The "my project will not start" impression is created by the alarm modal taking focus; clicking Acknowledge reveals that the runtime is in fact running.

Case B: Project Freezes on Start Screen After the Alarm

Less commonly, the runtime appears frozen immediately after the license alarm is acknowledged. The project does not resolve to the configured start screen. Causes observed in the field include:

• BackgroundService delay. The Siemens Automation License Manager service is still starting when Start RT is invoked. The runtime times out the ALM query after ~3 seconds and posts the alarm, but the runtime UI is not yet ready to draw. Retrying Start RT after 10–20 seconds resolves the issue.
• Antivirus interference. Endpoint protection software that blocks almsrv.exe from reading the license storage path %ProgramData%\Siemens\Automation\LicenseServer\ produces the same symptom. Adding an exception for the ALM folder and service fixes it.
• Port 20008 conflict. Another process on the engineering station has bound TCP/20008. The runtime listener fails to start, and the runtime hangs in initialization.
• TIA Portal version skew. The TIA Portal ES version (V17/V18/V19/V20/V21) and the WinCC Unified Runtime version installed for simulation are not the same minor release. The container format is incompatible, and the runtime silently fails to deserialize the project.

Step-by-Step Resolution Procedure

Use this procedure to convert the license alarm into a clean, repeatable simulation start. The procedure assumes TIA Portal V20 or V21 and a project that compiles without errors. For V17 the same sequence applies, but the menu paths in step 1 differ.

1. Verify the runtime installation. Open Control Panel → Programs and Features and confirm that SIMATIC WinCC Unified PC RT (matching your TIA Portal major version) is installed. If only the ES package is present, install the RT package from the TIA Portal installation media or from the Siemens Online Software Delivery portal.
2. Verify the Automation License Manager service. Open services.msc and confirm that the service Siemens Automation License Manager is set to Automatic and is in the Running state. If it is stopped, start it and wait for the state to settle before continuing.
3. Check port 20008. Open an elevated command prompt and run netstat -ano | findstr :20008. If a foreign process is bound to the port, either stop that process or change the ES↔RT port in the project properties (TIA Portal Runtime settings → Communication → Port).
4. Confirm antivirus exceptions. Add the following paths to your endpoint protection exclusion list:
   • C:\Program Files\Siemens\Automation\WinCCUnified\
   • C:\Program Files (x86)\Siemens\Automation\LicenseServer\
   • %ProgramData%\Siemens\Automation\
5. Compile the project fully. In the TIA Portal project tree, right-click the HMI device → Compile → Software (complete rebuild). A full rebuild forces the runtime container to be regenerated and removes version-skew artifacts.
6. Start the simulation. Right-click the HMI device → Start RT. The Unified PC RT loader starts. The license alarm appears. Acknowledge it.
7. Wait for the start screen. Allow up to 10 seconds for the runtime to draw the configured start screen. The runtime is in demo mode; the project is fully operable.
8. (Optional) Install a license key. To remove the alarm, install a valid WinCC Unified PC RT license into the ALM. Use the Siemens Automation License Manager, the ALM Web Interface at https://localhost:44100, or the aksusb.exe command-line tool for USB dongles. Restart the simulation; the alarm no longer appears.

Verifying Successful Simulation

Use the following checks to confirm the runtime is healthy, in addition to looking for the absence of the license alarm in the runtime control log.

Unified Comfort Panel Simulation Alternative

If the project is destined for a Unified Comfort Panel (MTP700 Unified, MTP1000 Unified, MTP1200 Unified, MTP1500 Unified, MTP1900 Unified, MTP2200 Unified, or the second-generation Unified Comfort Panels with article numbers 6AV2 128-xxx), the engineer can simulate without ever seeing the license alarm. The conditions are:

1. The active TIA Portal project must be a Unified Comfort Panel device, not a PC station.
2. The SIMATIC WinCC Unified PC RT package must not be installed on the engineering station. If it is installed, the simulator preferentially loads the PC RT engine, and the license alarm appears.
3. The Comfort Panel RT is bundled with the TIA Portal Unified ES installer. No additional license key is required for local simulation.

With those conditions met, Start RT launches the Comfort Panel RT simulator directly, opens the ES↔RT channel on TCP/20008, and renders the panel layout at the configured resolution. No ALM check is performed, no alarm is raised, and the runtime operates indefinitely without a reminder timer.

Communication Path and Port 20008

The TIA Portal ES↔RT communication channel is a TCP connection on a fixed port. Per the TIA Portal V20 and V21 documentation, the Unified simulation uses Ethernet port 20008. The port is opened by the runtime on the configuration PC, and the TIA Portal engineering client connects to it for online diagnostics, tag forcing, and project download operations.

Network and firewall requirements:

• Port 20008 must be open on the loopback interface (always the case on a single engineering station).
• If the engineer wishes to connect a TIA Portal client on a different machine to a remote runtime (e.g., a Unified IPC on the plant network), port 20008/TCP must be open in the Windows firewall of the runtime PC and in any intermediate network firewalls.
• The port is configurable from the TIA Portal project tree under Runtime settings → Communication → Port. If a non-default port is configured, the documentation must be updated in the project handoff package.
• Only one runtime instance can bind to a given port at a time. Multiple parallel simulations on the same engineering station require distinct ports per project.

Cross-Version Behavior (V17, V20, V21)

WinCC Unified has evolved across TIA Portal V17, V18, V19, V20, and V21. The license check at simulation start has been consistent across all of these versions, but other behavior differs.

Troubleshooting Matrix

Use this matrix to map observed symptoms to the most likely root cause and the corresponding remedy.

Cross-Platform Notes

Although WinCC Unified is Windows-only, the licensing mechanics are the same on Windows 10 IoT Enterprise LTSC 2019, Windows 10 IoT Enterprise LTSC 2021, Windows 11, Windows Server 2019, and Windows Server 2022. The ALM service is identical across all supported platforms. The only platform-specific caveat is that Windows Server editions require the Desktop Experience feature for the runtime UI to render; the Server Core install option is not supported for Unified PC RT.

Virtualization is fully supported. Engineers running TIA Portal in a Hyper-V or VMware VM with a USB license dongle must use the ALM network license server configuration; the local ALM cannot read a USB key plugged into a different physical host. The standard pattern is to run the ALM service on a small always-on VM and have the engineering VM and the runtime VM both pull the license from the network ALM.

Frequently Asked Questions