Resolving Missing Simulation Units and Admin Dialog Failures in SIMIT After Windows 10 Updates

In SIMIT V10.2 Upd2 (and V10.1 Upd2), when Simulation Units (formerly SIMBA hardware boxes) become invisible in SIMIT couplings, fail discovery in the SU Administration console, and log the Trace Viewer error 'failed to finish loading admin dialog' following Windows 10 cumulative updates, the failure is caused by User Account Control (UAC) token restriction blocking local loopback RPC communication. To resolve the error, launch SIMIT by right-clicking the application icon and selecting 'Run as administrator', ensure the Windows service 'Simulation Unit Service' is running and configured for Automatic startup, and verify that the simulation network adapter profile is set to Private or Domain.

Executive Summary

Hardware-in-the-loop (HIL) simulation utilizing Siemens Simulation Units (PN/DP Simulation Units, formerly SIMBA) allows automation teams to test real controller execution against virtual field I/O at wire speed. Following the installation of monthly Microsoft Windows 10 cumulative security updates, commissioning engineers frequently discover that previously working simulation benches abruptly break: SIMIT fails to discover Simulation Units in coupling dialogs, SU Administration crashes on launch, and SIMIT Trace Viewer logs failed to finish loading admin dialog. Despite the fact that PRONETA and Windows ping discover the hardware normally, SIMIT cannot connect. This article explains the underlying UAC and RPC loopback restrictions introduced by Windows updates and details the administrative remediation procedure.

Architecture and Fundamental Mechanics

SIMIT Communication Architecture, Simulation Unit RPC Daemon, and Windows UAC Security Policies:

Architecture of SIMIT Simulation Unit Coupling:
SIMIT couples with physical Simulation Units over standard Industrial Ethernet (PROFINET / PROFIBUS emulation).
The physical hardware discovery and channel assignment are mediated by the Simulation Unit Administration Engine and its background daemon: SimulationUnitService.exe (or SimbaServer.exe).
SIMIT communicates with this administration daemon via local Windows Remote Procedure Calls (RPC) and Named Pipes.
The Impact of Windows 10 Cumulative Security Updates:
Recent Windows 10 security rollups implement stricter Remote Procedure Call (RPC) Filter Rules and enforce restrictive User Account Control (UAC) token filtering for processes attempting loopback device enumeration.
When SIMIT is launched by double-clicking the desktop icon under standard user privileges, Windows assigns it a filtered, non-elevated security token.
When SIMIT calls the Simulation Unit administration API to open the coupling dialog, the RPC request is blocked by Windows security. The internal UI constructor crashes, logging failed to finish loading admin dialog in SIMIT Trace Viewer.
Network Profile Classification (Public vs Private):
Windows updates frequently reset unauthenticated network adapters (such as dedicated simulation network cards) to the Public firewall profile, which blocks Layer 2 broadcast discovery telegrams used by SIMIT to enumerate Simulation Unit hardware.

Step-by-Step Implementation Procedure

Enforce Administrative Elevation for SIMIT:
* Close SIMIT completely.
* Right-click the SIMIT desktop shortcut and select Properties.
* Switch to the Compatibility tab.
* Check the box: Run this program as an administrator.
* Click Apply and OK.
* Right-click the SIMIT icon and explicitly select Run as administrator.
Verify and Restart the Simulation Unit Windows Service:
* Press Win + R, type services.msc, and press Enter.
* Locate Simulation Unit Service (or Simba Server Service).
* Verify that the status is Running and startup type is Automatic.
* Right-click the service and select Restart.
Configure Network Adapter Firewall Profile to Private:
* Open Windows PowerShell as Administrator.
* Execute Get-NetConnectionProfile to view active network adapters.
* Locate the network adapter connected to the Simulation Unit.
* If NetworkCategory is Public, execute:
powershell Set-NetConnectionProfile -InterfaceAlias "<AdapterName>" -NetworkCategory Private
* This unblocks local broadcast discovery ports.
Test Discovery in Simulation Unit Administration:
* Open Windows Start Menu, navigate to Siemens Automation, right-click Simulation Unit Administration, and select Run as administrator.
* Confirm that the administration dialog opens cleanly without trace exceptions.
* Click Scan Network; confirm that all physical Simulation Units appear with green status indicators.
Re-establish SIMIT Coupling:
* Launch SIMIT as Administrator.
* Open your simulation project; open the Simulation Unit coupling.
* Confirm that all Simulation Units populate in the dropdown list and assign I/O channels.

Verification

In SIMIT, launch the simulation (Simulation > Start); verify that the Simulation Unit coupling status turns solid green.
Observe the physical TX/RX LEDs on the Simulation Unit hardware blinking rapidly, confirming active PROFINET frame generation.
Open SIMIT Trace Viewer; confirm that zero RPC timeout or 'failed to finish loading admin dialog' exceptions are logged.

Limitations and Operational Precautions

Downgrading SIMIT versions does not resolve the failure because the restriction originates in the Windows 10 RPC security baseline. Always run SIMIT with elevated administrator privileges when interfacing with hardware Simulation Units.

Engineer FAQ

Why did SIMIT stop discovering Simulation Units after Windows 10 updates?

Windows cumulative security updates enforced stricter UAC token filtering on local RPC calls, blocking non-elevated SIMIT processes from binding to the Simulation Unit daemon.

How do I fix 'failed to finish loading admin dialog' in SIMIT?

Launch SIMIT using 'Run as administrator' and ensure the 'Simulation Unit Service' is running in Windows Services.

Why can PRONETA see the Simulation Unit while SIMIT cannot?

PRONETA uses raw WinPcap/Npcap network capture drivers that bypass Windows RPC policies, whereas SIMIT relies on the local Simulation Unit Service RPC daemon.