Fixing LOGO!Soft Comfort V5/V6 Java Fatal Error on Windows 7

Problem Overview

Engineers and students attempting to install LOGO!Soft Comfort V5.0.x or V6.0.x on a Windows 7 workstation encounter two blocking errors during setup:

1. Fatal Application Error - "Unable to launch Java application (unable to locate application's 'main' class)."
2. Installer extraction failure - "Please select another location to extract the installer to."

The installer halts before any Setup.exe can run, leaving the LOGO! programming environment unusable and preventing any program download to a LOGO! logic module (6ED1 052-xxx00-0BA series for V5, 6ED1 055-xxx00-0BA0 series for V6-era hardware). This article documents the root cause, the verified OS-compatibility matrix, and the field-proven resolution path.

Affected Software and Hardware

The version history above is confirmed by the LOGO!Soft Comfort V5.0 Online Help (PDF) and the current Siemens product support tree at Siemens Industry Online Support.

Root Cause Analysis

Why the Java fatal error appears

LOGO!Soft Comfort V5.0 and V6.0 installers use a Java-based bootstrap. The bootstrap reads a packaged .jar archive that contains the installer's main class, then invokes it through the bundled JRE (jre/bin/java.exe). On Windows 7 three independent failures break the chain:

1. JRE version mismatch - The bundled Java runtime is older than Java 5u22. Windows 7's user-mode hook chain rejects the obsolete java.dll shim, and the launcher cannot resolve META-INF/MANIFEST.MF.
2. UAC virtualization - When the installer is launched from a path under C:\Program Files or C:\Users\<name>\Downloads by a non-elevated user, Windows 7 silently virtualizes the write target. The extracted .class files land in %LOCALAPPDATA%\VirtualStore and the main-class loader cannot find them at the original path.
3. Long-path / 8.3 name resolution - LOGO!Soft Comfort V5 expects short (8.3) DOS-compatible path names. User profiles on Windows 7 typically contain spaces and exceed the legacy path limit, producing the "Please select another location to extract the installer to" prompt.

Why the installer extraction prompt appears

The "Please select another location to extract the installer to" message is generated by the Java installer wrapper (InstallAnywhere-derived code). When the bootstrap cannot write to %TEMP%\LogoComfort_Install because the volume is NTFS-compressed, encrypted with EFS, or located on a redirected folder, the wrapper aborts extraction. This is independent of the JRE issue and must be fixed separately.

Why the program class cannot be located

The exact error text - "unable to locate application's 'main' class" - is emitted by the JavaWS / javaw.exe launcher when the manifest attribute Main-Class is missing or the referenced .class is not on the classpath. With the V5/V6 installer, this means the bootstrap .jar itself was extracted incompletely. The user sees the Java error first because the manifest check runs before the installation wizard draws any UI.

Compatibility Matrix

This matrix is consistent with the platform requirements documented in LOGO!Soft Comfort V5.0 Online Help (PDF, A5E00130839-04) and the current LOGO! product manual at Siemens Industry Online Support.

Resolution Path 1 - Upgrade to LOGO!Soft Comfort V7 (Recommended)

The cleanest, fully supported path is to replace the legacy V5/V6 installation with LOGO!Soft Comfort V7.0 or later. V7 was the first revision explicitly engineered for Windows 7 and ships a self-contained installer that no longer relies on the Java bootstrap. The official Siemens knowledge base article that documents the supported update procedure is referenced at Siemens Support Entry 17164153 - Update installation of LOGO!Soft Comfort without installed LOGO! software.

Prerequisites for V7 upgrade

• Windows 7 SP1 (32-bit or 64-bit) with all current Windows updates
• Administrator account on the target machine
• Minimum 350 MB free disk on the system drive
• .NET Framework 3.5 SP1 (enabled via "Programs and Features - Turn Windows features on or off")

Step-by-step V7 upgrade

1. Disconnect any LOGO! logic module from the PC USB or serial port.
2. Open Control Panel -> Programs and Features and uninstall any prior LOGO!Soft Comfort entry. If V5/V6 was partially installed, also remove residual Siemens entries under HKEY_LOCAL_MACHINE\SOFTWARE\Siemens using regedit.
3. Download the current LOGO!Soft Comfort V7 installation package from the Siemens LOGO! application-examples page at LOGO! application examples.
4. Right-click Setup.exe and choose Run as administrator. Accept the UAC prompt.
5. Select an installation path without spaces (for example C:\Siemens\LogoComfortV7) and click Install.
6. Restart the workstation when prompted - the LOGO!Soft Comfort service LogoComfortService.exe is registered at first boot.
7. Launch LOGO!Soft Comfort V7, choose Tools -> Options -> Interface, and select the correct COM port or USB driver for your LOGO! hardware (LOGO! 8 uses the LOGO! USB Driver PID 0x0801).
8. Open or import any existing .lsc or .lld project - V7 reads V5/V6 program files directly without conversion.

Resolution Path 2 - Force V5/V6 to Install on Windows 7 (Compatibility Mode)

If a school or training requirement mandates keeping V5 or V6 (for example, to read legacy .lsc files that have macro libraries which do not import cleanly into V8), the installer can be forced to run under the Windows XP compatibility shim. This is officially undocumented by Siemens and is provided as a field workaround only.

Procedure

1. Copy the LOGO!Soft Comfort V5 or V6 installation files to C:\LogoInstall\ - the root of an NTFS drive without compression, EFS, or path longer than 80 characters.
2. Right-click Setup.exe, choose Properties -> Compatibility.
3. Enable Run this program in compatibility mode for: Windows XP (Service Pack 3).
4. Check Run as administrator and click Apply.
5. Open an elevated command prompt (cmd -> Run as administrator) and install an updated Java runtime that the installer can fall back to:
   java -version (verify Java 7 update 80 or Java 8 update 202 is installed).
   If absent, install Java 7 Update 80 (32-bit) - this is the last JRE that still ships the legacy java.exe launcher paths used by the V5/V6 bootstrap.
6. Set the environment variable JAVA_HOME to the new JRE root and add %JAVA_HOME%\bin to PATH.
7. From the elevated command prompt, navigate to C:\LogoInstall\ and run Setup.exe.
8. If the "Please select another location to extract the installer to" prompt appears, change the extraction directory to C:\LogoInstall\Temp (must exist and be writable by the Administrators group).

What to expect

The Java fatal error is normally cleared once JAVA_HOME is exported system-wide. The installer then completes, but the LOGO!Soft Comfort IDE itself may still refuse to start because the JNLP cache is missing. Clear the cache once after install:

Launch LOGO!Soft Comfort V5 or V6 from the Start menu - the IDE should now load the project workspace.

Verification

Functional check

1. Open LOGO!Soft Comfort and create a new project using the correct LOGO! family for your hardware:
   - LOGO! 8 (6ED1052-1xx08-0BA0) requires LOGO!Soft Comfort V8.0 or later.
   - LOGO! 7 (6ED1052-1xx07-0BA0) is supported by V7.0 or later.
   - LOGO! 0BA6 / 0BA5 is supported by V6/V7.
2. Drag an On-delay function block (B001) and an Input I1 onto the FBD canvas.
3. Wire I1 -> B001 trigger, B001 output -> Q1.
4. Press F5 (Simulation). The block should toggle after the configured delay of 5 s.
5. Press F4 (Online Test) with a LOGO! connected. Status flags should appear green on the simulated contacts.

Driver check

Open Device Manager and confirm the LOGO! USB device appears under Ports (COM & LPT) as Siemens LOGO! USB (COMx). If the entry shows a yellow triangle, right-click, choose Update Driver, and point to C:\Siemens\LogoComfort\USBDriver or the equivalent V5/V6 installation directory.

Communication check

In LOGO!Soft Comfort choose Tools -> Transfer -> PC -> LOGO!. The dialog should report PC <-> LOGO! OK within 3 s. A timeout indicates the Ethernet or USB cable is not seated, or the firewall is blocking UDP port 13500 (used by LOGO! 8 for Ethernet auto-discovery).

Common Fault Matrix

Choosing Between V6 and V8 for a School Project

The source question compared LOGO! against raw microcontrollers (AVR, PIC). For an educational project the relevant comparison is between the supported LOGO!Soft Comfort version on the available PC and the LOGO! hardware on the lab bench.

For a school project that needs to demonstrate high-level industrial-grade control - for example, a pump-sequencer with analog level sensing - the LOGO! route delivers a working, certified system in days. The microcontroller route delivers deeper embedded knowledge but typically does not match the industrial-grade specification in a single-semester timeline.

Step-by-Step: Migrating an Existing V5/V6 Project to V7

1. Open the project in the originally installed V5 or V6.
2. Choose File -> Save As and confirm the format .lsc (LOGOSoft V5) or .lld (ladder diagram V6).
3. Install LOGO!Soft Comfort V7 side-by-side on a Windows 7 machine.
4. In V7, choose File -> Open and select the .lsc or .lld file.
5. V7 displays a conversion summary. Click OK.
6. Recompile (F5) and verify simulation matches the V5/V6 behavior.
7. Save as .lsc7 for future V8 compatibility.

Field-Commissioned Caveats

• USB driver signing: Windows 7 x64 with Secure Boot enabled rejects the unsigned V5 USB driver. Either disable driver-signing enforcement (test mode: bcdedit /set testsigning on) or use a 32-bit Windows 7 installation for V5/V6.
• User profile path: Avoid C:\Users\First Last\AppData\Local\Temp as the extraction target. User names with non-ASCII characters break the Java manifest parser.
• Antivirus: Many endpoint protection suites quarantine the Java bootstrap executable (JavaLauncher.exe) inside the LOGO! install media. Whitelist the install directory before re-running Setup.
• Parallel installs: Installing V5, V6, and V7 on the same Windows 7 image is supported, but the COM-port mapping may shift between IDEs. Always check Tools -> Options -> Interface after each install.
• Windows 7 end-of-support: Microsoft ended mainstream support for Windows 7 on January 14, 2020, and extended security updates ended January 10, 2023. For new installations, target Windows 10 22H2 or Windows 11 with LOGO!Soft Comfort V8.4.

Recommended Configuration by Use Case

FAQ