Hi @Obada Ahmad AlAasasi , Welcome to Microsoft Q&A,
Judging from the error message, it seems that you have encountered the problem that the "System.Diagnostics.EventLog.dll" assembly cannot be found in the specified directory. The "PosExplorer" class you are using probably depends on this assembly.
Make sure you reference the "System.Diagnostics.EventLog.dll" assembly in your project. In Visual Studio, right-click your project, select Add->Reference, and check that the necessary assembly is included. Set the "Copy Local" property of the "System.Diagnostics.EventLog.dll" reference to "True". This ensures that the DLL is copied to the project's output directory during the build.
You also can refer to Event Handler Sample (POS for .NET v1.14 SDK Documentation)
Best Regards,
Jiale
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