need help in DES Decryption

I am trying to decrypt an encoded encrypted value. But it is not returning the unencrypted value. I am using DES algorithm.

Can someone please help me with this?

Decryption Code:

public static string Decrypt(string encryptedString)

{

byte[] bytes = CreateKey();

if (String.IsNullOrEmpty(encryptedString))

{

throw new ArgumentNullException

("The string which needs to be decrypted can not be null.");

}

DESCryptoServiceProvider cryptoProvider = new DESCryptoServiceProvider();

MemoryStream memoryStream = new MemoryStream

(Convert.FromBase64String(encryptedString));

cryptoProvider.Padding = PaddingMode.Zeros;

CryptoStream cryptoStream = new CryptoStream(memoryStream,

cryptoProvider.CreateDecryptor(bytes, bytes), CryptoStreamMode.Read);

StreamReader reader = new StreamReader(cryptoStream);

return reader.ReadToEnd();

}