private void btnLoadPicture_Click(object sender, EventArgs e)
        {
            OpenFileDialog OF = new OpenFileDialog();
            OF.Title = "Bitte Bild wählen...";
            OF.Multiselect = false;
            OF.Filter = "Bilder|*.jpeg;*.jpg;*.png;*.bmp|JPG-Bilder|*.jpeg;*jpg|PNG-Bilder|*.png|BMP-Bilder|*.bmp";
            DialogResult DR = OF.ShowDialog();

            if (DR == DialogResult.OK)
            {
                iContactPicture = Image.FromFile(OF.FileName);
                pictureContact.Image = iContactPicture;
            }
            else
            {
                pictureContact.Image = global::Personaldaten.Properties.Resources.Who_is_it;
            }
        }

 private string ImageToString(Image img, ImageFormat imgFormat)
        {
            string sImg;
            MemoryStream MS = new MemoryStream();
            img.Save(MS, imgFormat); //Hier tritt der Fehler auf!!!!
            sImg = Convert.ToBase64String(MS.ToArray());
            MS.Close();
            return sImg;
        }

        private string ImageToString(string imagePath, ImageFormat imgFormat)
        {
            string sImg;
            using(MemoryStream memoryStream = new MemoryStream())
            using(Image img = Image.FromFile(imagePath))
            {
               img.Save(memoryStream, imgFormat);
               sImg = Convert.ToBase64String(memoryStream.ToArray());
            }
            return sImg;
        }

pictureContact.Image = global::Personaldaten.Properties.Resources.Who_is_it;

public void SetGeneralVars(string sSpitzname, string sTitel, string sBirthday, Image contactPicture)
        {
            this.sSpitzname = sSpitzname;
            this.sTitel = sTitel;
            this.sBirthday = sBirthday;
            this.sContactPicture = ImageToString(contactPicture, contactPicture.RawFormat);
        }

        private string EncodeImageBase64(Image img, ImageFormat imgFormat)
        {
            byte[] imageContents;


            using (MemoryStream memoryStream = new MemoryStream())
            using (Image tempImage = new Bitmap(img))
            {
                tempImage.Save(memoryStream, imgFormat);
                imageContents = memoryStream.ToArray();
            }

            return Convert.ToBase64String(imageContents);
        }

        private void button1_Click(object sender, EventArgs e)
        {
            textBox1.Text = EncodeImageBase64(pictureBox1.Image, ImageFormat.Jpeg);
        }

        private void FrmOp_AcceptOpenFrame(string sFile)
        {
            tabControl1.Visible = true;
            btnPreview.Visible = true;
            lblChoice.Visible = false;
            btnSave.Visible = true;

            Kontakt k = new Kontakt();
            k = Kontakt.OpenContact(sFile,sKey,sIv);
            this.txtName.Text = k.sName;
            this.txtFirstName.Text = k.sFirstName;
            this.txtTitel.Text = k.sTitel;
            this.txtSpitzname.Text = k.sSpitzname;
            if (k.bIsFemale)
            {
                this.rbtnFemale.Checked = true;
            }
            else { this.rbtnMale.Checked = true; }
            this.iContactPicture = Kontakt.StringToImage(k.sContactPicture);
            this.pictureContact.Image = iContactPicture;

        public static Image StringToImage(string sImage)
        {
            MemoryStream MS = new MemoryStream(Convert.FromBase64String(sImage));
            Image img = Image.FromStream(MS);
            MS.Close();
            return img;
        }