encryption and decryption

hi friends
 iam encrypting a captacha code and iam facing a problem of error :



Invalid length for a Base-64 char array.

below is my code :


public static string Encrypt(string stringToEncrypt, string sEncryptionKey)
        {
            byte[] key = { };

            byte[] IV = { 10, 20, 30, 40, 50, 60, 70, 80 };

            byte[] inputByteArray; //Convert.ToByte(stringToEncrypt.Length)

            try
            {
                k ...