FFMPEG Does not work on Windows Server 2008

I have an ASP.NET MVC Web Site ,the user can upload a video and When Done It finish uploading I show him an image extracted from the Video, To do this I used the FFMPEG exe to get a frame. Everthing works well in the developement machine , when I use the test environement it does not work!! I've given the read/write and execute permissions to following folders: 1. videos(folder that store uploaded video files) 2. thumbnails (folder that store the thumbnails of videos, captured by ffmpeg) 3.ffmpeg.exe file at root and given read/write execute permissions to that file also. but it does not work.

 var _converter = new ImageConvertor(@System.Configuration.C开发者_StackOverflow社区onfigurationManager.AppSettings["FFmpegExec"].ToString());
            _converter.WorkingPath = Server.MapPath("~/VideoSamples");
            OutputPackage oo = _converter.ConvertToFLV(videoFilepath);
            FileStream outStream = System.IO.File.OpenWrite(Path.Combine(Server.MapPath("~/VideoSamples"), id.ToString() + ".flv"));
            oo.VideoStream.WriteTo(outStream);

This Code Works on developement env but not in test env !!! Any Ideas Please