Such a nasty issue may happen to everyone: you want to delete the folder, but you can’t, because it is being used by an other process. The following C# code shows how to find this process, which you may want to terminate later on.

• Download sysinternals-suite from microsoft
• Find a path to handle.exe in sysinternals-suite
• Run C# code

// Define the path of the folder you want to delete
string folderPath = @"C:\[YOUR_FOLDER]";

// Run the Handle tool to find out which process is using the folder
Process handleProcess = Process.Start(new ProcessStartInfo
{
    FileName = "C:\\[PATH_TO_HANDLE]\\handle.exe",
    Arguments = $"-accepteula {folderPath}",
    UseShellExecute = false,
    RedirectStandardOutput = true
});

// Read the output of the Handle tool
string output = handleProcess.StandardOutput.ReadToEnd();

// Display the output
Console.WriteLine(output);