testing with LinqPad, it shows a parameter error

[Davider]

I'm using LinqPad to test the following code, and it gives me a parameter error
PS: I have already set the environment variables correctly, and the path mentioned in the error is correct.

error info:
Parameter error: 'C:\Users\Administrator\Desktop\DLL\ffmpeg.exe'

Linqpad C# Code:

using Xabe.FFmpeg;

async Task Main()
{
	string inputPath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Desktop), "a.mpg");
	string outputPath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Desktop), "a.mp4");

	var conversion = Xabe.FFmpeg.FFmpeg.Conversions.New();

	var snippet = await FFmpeg.Conversions.FromSnippet.Convert(inputPath, outputPath);
	IConversionResult result = await snippet.Start();
}