image not opening after ffmpeg saving

In my project I am saving videos, converting formats to .swf using ffmpeg. Converting and saving the videos is working fine, but I have a problem with creating the thumbnails. It saves a "picture.jpg" but there is no image. looking at the thumbnail its only got the normal photoviewer sign which is fine, but when I try to open the image it gives a message of  Windows photo viewer: Windows photo viewer cant open this picture because the file appears to be damaged, corrupted, or is too large. (this image is 2.7MB) - Photos taken from my camera is about 5MB and that opens.

PictureViewer: couldn't display "image.jpg" because a suitable graphics importer could not be found.

Paint: Paint cannot read this file. This is not a valid bitmap file or its format is currently not supported. The images won't open in any I done to save the image:

string thumbpath, thumbname;
            string thumbargs;
            string thumbre;
            thumbpath = Server.MapPath("~\\uploads\\" + dtYear + "\\" + dtMonth + "\\Thumb\\");

            CreateDirectoryIfNotExists(thumbpath);

            // Create the path and file name to check for duplicates.
            pathToCheck = thumbpath;

            // Create a temporary file name to use for checking duplicates.
            tempfileName = "";

            // Check to see if a file already exists with the
            // same name as the file to upload.        
            if (System.IO.File.Exists(pathToCheck))
            {
                int counter = 2;
                while (System.IO.File.Exists(pathToCheck))
                {
                    // if a file with this name already exists,
                    // prefix the filename with a number.
                    tempfileName = thumbpath + counter.ToString() + withoutext + ".jpg";
                    pathToCheck = tempfileName;
                    counter++;
                }

                outputfile = tempfileName;
                // Notify the user that the file name was changed.
                lblMsg.Text = "A file with the same name already exists." +"<br />Your file was saved as " + counter.ToString() + withoutext + ".jpg";
            }

            thumbname = thumbpath + withoutext + "%d" + ".jpg";
            Session["thumbname"] = withoutext + "1" + ".jpg";
           // thumbargs = "-i {0} -f image2 frame-%1d.png -y {1};
            thumbargs = "-i " + inputfile + " -f image2 frame-%1d.jpg -y " + thumbname;
            Process thumbproc = new Process();
            thumbproc.StartInfo.FileName = spath + "\\ffmpeg\\ffmpeg.exe";
            thumbproc.StartInfo.Arguments = thumbargs;
            thumbproc.StartInfo.UseShellExecute = false;
            thumbproc.StartInfo.CreateNoWindow = false;
            thumbproc.StartInfo.RedirectStandardOutput = false;
            try
            {
                thumbproc.Start();
                fuPath.PostedFile.SaveAs(thumbname);
            }
            catch (Exception ex)
            {
                Response.Write(ex.Message);
            }
            thumbproc.WaitForExit();
            thumbproc.Close();

I have tried a few ways with the arguments, but with no success:

 //thumbargs = "-i " + inputfile + " -an -ss 00:00:03 -s 120×90 -vframes 1 -f mjpeg " + thumbName;
               // thumbargs = "-i " + inputfile + "-f image2 -ss 1.000 -vframes 1 " + thumbName;
                thumbargs = "-i " + inputfile + " -vframes 1 -ss 00:00:10 -s 150x150 " + thumbName;

                //  thumbargs = "ffmpeg -i" + inputfile + " -ss 0:00:01.000 -sameq -vframes 1 " + withoutext + ".jpg";
                //  thumbargs = "-i " + inputfile + " -vframes 1 -ss 00:00:07 -s 150x150 " + thumbName;
                Process thumbproc = new Process();

This is how it looks like when I want to open the image: (it may be that it is saving an empty image?)

EDIT:

I changed a bit of my code. Debugging through my code there is no exception that is thrown, but if I point the mouse over the process (after it started) it  "shows an exception of type System.InvalidOperationException"

thumbargs = "-i "+ postedfilename +" vframes 1"+ thumbName;
                ProcessStartInfo thumbProcstartIfo =new ProcessStartInfo();
                thumbProcstartIfo.FileName =@"\ffmpeg\ffmpeg.exe";
                thumbProcstartIfo.Arguments = thumbargs;
                thumbProcstartIfo.UseShellExecute =false;
                thumbProcstartIfo.CreateNoWindow =true;
                thumbProcstartIfo.RedirectStandardOutput =false;

               try
                {
                   using (var process =new Process())
                    {
                        process.StartInfo = thumbProcstartIfo;
                        process.Start();
                        process.WaitForExit();
                    }
                }
               catch (InvalidOperationException ex)
                {
                    lblMsg.Text = ex.ToString();
                }

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