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Error: ClassNotFoundException – cz.winstrom.vo.WSLokCiselnik

Error backing up company – unable to load part of the application

Written by Petr Pech

This error means that the application is unable to load a required program component (class). This is most commonly caused by a corrupted or blocked file in the ABRA Flexi installation.

In the past, we have identified the following file as the cause:
winstrom-core-2020.x.jar (located in the ...\WinStrom\lib folder)


Most common causes:

  • corrupted Flexi installation

  • blocked file (antivirus / firewall)

  • incomplete update


How to resolve the issue (recommended steps):

  1. Uninstall ABRA Flexi

  2. Restart your computer

  3. Verify that:

    • the Winstrom Service service has been removed

    • the installation directory has been deleted (e.g. C:\Program Files (x86)\WinStrom)

  4. Perform a fresh installation of ABRA Flexi


If the issue persists:

  • contact technical support and provide:

    • the file winstrom-core-2020.x.jar

    • the file server-impl.txt

The file server-impl.txt can be found in the installation folder (the path can be looked up in the registry):

  • HKLM\SOFTWARE\FlexiInstallDir

  • or HKLM\SOFTWARE\Wow6432Node\FlexiInstallDir

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