Process throws System.InvalidOperationException

filargs = "C:\\Program Files\\ffmpeg\\ffmpeg.exe -i " + inputfile + " -ar 22050 " + outputfile;

string spath;
spath = Server.MapPath(".");
ProcessStartInfo procStartIfo = new ProcessStartInfo();
procStartIfo.FileName = "C:\\Program Files\\ffmpeg\\ffmpeg.exe";
procStartIfo.Arguments = filargs;
procStartIfo.UseShellExecute = false;
procStartIfo.CreateNoWindow = false;
procStartIfo.RedirectStandardOutput = true;

try
{
    var process = new Process();

        process.StartInfo = procStartIfo;
        process.Start();
        process.WaitForExit();

}