Ghostscript rasterizer.GetPage returns null c#

I´m trying to get an image from PDF with Ghostcript.NET in C#. I have installed Ghostscript dll already (both 32 and 64 bit) and added the reference in the proyect. I´ve just taken the example for the web and it gives me an error (img was null) and i don´t know why. This is the code:

`using System;
using Ghostscript.NET.Rasterizer;
using System.IO;
using Ghostscript.NET;
using System.Drawing.Imaging;

namespace StackOverflowExample
{
    class Program
    {
 
        static void Main(string[] args)
        {
            int desired_dpi = 96;

            string inputPdfPath = @"C:\Users\orubio\Documents\Pruebas\test.pdf";
            string outputPath = @"C:\Users\orubio\Documents\Pruebas\";

            GhostscriptVersionInfo gvi = new GhostscriptVersionInfo(@"C:\Program Files (x86)\gs\gs9.56.1\bin\gsdll32.dll");

            using (var rasterizer = new GhostscriptRasterizer())
            {
                rasterizer.Open(inputPdfPath, gvi, false);

                for (var pageNumber = 1; pageNumber <= rasterizer.PageCount; pageNumber++)
                {
                    var pageFilePath = Path.Combine(outputPath, string.Format("Page-{0}.png", pageNumber));

                    var img = rasterizer.GetPage(desired_dpi, pageNumber);
                    img.Save(pageFilePath, ImageFormat.Png);

                    Console.WriteLine(pageFilePath);
                }
            }

        }
    }
}`

img null error

Ty everyone :D