invalid length for a base 64 char array

[vbbit]

Hi I have a code below, but everytime, my "text" throwing an error invalid length for a base 64 char array, and I don't know how to fix this.

try
            {
                key = Encoding.UTF8.GetBytes(stringKey.Substring(0, 8));
                DESCryptoServiceProvider des = new DESCryptoServiceProvider();
                Byte[] byteArray = Convert.FromBase64String(text);
                MemoryStream memoryStream = new MemoryStream();
                CryptoStream cryptoStream = new CryptoStream(memoryStream,
                    des.CreateDecryptor(key, IV), CryptoStreamMode.Write);
                cryptoStream.Write(byteArray, 0, byteArray.Length);
                cryptoStream.FlushFinalBlock();
                return Encoding.UTF8.GetString(memoryStream.ToArray());
            }
            catch (Exception ex)
            {
                // Handle Exception Here
            }
            return string.Empty;