The input data is not a complete block.

private string Decrypt(string cipherText)

{

string EncryptionKey = "MAKV2SPBNI99212";

//byte[] cipherBytes = Convert.FromBase64String(cipherText.Replace(" ","+"));

byte[] cipherBytes = Encoding.ASCII.GetBytes(cipherText.Replace(' ','+'));

using (Aes encryptor = Aes.Create())

{

Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(EncryptionKey, new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 });

encryptor.Key = pdb.GetBytes(32);

encryptor.IV = pdb.GetBytes(16);

using (MemoryStream ms = new MemoryStream(cipherBytes))

{

using (CryptoStream cs = new CryptoStream(ms, encryptor.CreateDecryptor(), CryptoStreamMode.Write))

{

using (StreamWriter sr = new StreamWriter(cs))

{

cs.Write(cipherBytes, 0, cipherBytes.Length);

cs.FlushFinalBlock();

}

}

cipherText = Encoding.Unicode.GetString(ms.ToArray());

}

}

return cipherText;

}