AES 128 -bit Encryption-Decryption in C#

Question

I am trying to decrypt the given text with the key but i am getting error "The input data is not a complete block"    Check  code below and help if you can .

private string DecryptOTP(string decryptethis)
{
decryptethis = "4931cb6f11c9f8b24f0b05f9ec9a2cc0";
string decryptionKey = string.Empty;
decryptionKey = "f22704b8bc0dcc606303b5eb97332630";
byte[] cipherBytes = Convert.FromBase64String(decryptedOTP.Trim());
using (Aes encryptor = Aes.Create())
{
Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(decryptionKey.Trim(), 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())
{
using (CryptoStream cs = new CryptoStream(ms, encryptor.CreateDecryptor(), CryptoStreamMode.Write))
{
cs.Write(cipherBytes, 0, cipherBytes.Length);
cs.Close();
}
decryptethis = Encoding.Unicode.GetString(ms.ToArray());
}
}
return decryptethis;
}