Decrypting a text using Rijndael

[3bood ghzawi]

Hi all, i have been using a Rijndael algorithm to encrypt and decrypt a sequence of bytes, but when i run the code i get the following exeption "Padding is invalid and cannot be removed.", this exeption belongs to decrypt function at line int decryptedByteCount = cryptoStream.Read(pTextBytes, 0, pTextBytes.Length); i writ my code here:

public static byte[] Encrypt(byte[] clearData)
{
System.Configuration.AppSettingsReader settingsReader = new AppSettingsReader();
//Get your key from config file to open the lock!
string key = (string)settingsReader.GetValue("SecurityKey", typeof(String));

        MD5CryptoServiceProvider hashmd5 = new MD5CryptoServiceProvider();
        byte\[\] keyArray = hashmd5.ComputeHash(UTF8Encoding.UTF8.GetBytes(key));
        hashmd5.Clear();

        Rijndael rijKey = Rijndael.Create();
        rijKey.Mode = CipherMode.ECB;
        rijKey.Padding = PaddingMode.PKCS7;
        MemoryStream ms = new MemoryStream();
        CryptoStream cs = new CryptoStream(ms,rijKey.CreateEncryptor(), CryptoStreamMode.Write); 
        cs.Write(clearData, 0, clearData.Length);
        cs.FlushFinalBlock();
        byte\[\] cipherTextBytes = ms.ToArray();
        ms.Close();
        cs.Close();

        return cipherTextBytes;
    }

    public static byte\[\] Decrypt(byte\[\] encryptedData)
    {
        System.Configuration.AppSettingsReader settingsReader = new AppSettingsReader();
        //Get your key from config file to open the lock!
        string key = (string)settingsReader.GetValue("SecurityKey", typeof(String));
        MD5CryptoServiceProvider hashmd5 = new MD5CryptoServiceProvider();
        byte\[\] keyArray = hashmd5.ComputeHash(UTF8Encoding.UTF8.GetBytes(key));
        hashmd5.Clear();

        Rijndael rijKey = Rijndael.Create();
        rijKey.Mode = CipherMode.ECB;
        rijKey.Padding = PaddingMode.PKCS7;
        MemoryStream memoryStream = new MemoryStream(encryptedData);
        CryptoStream cryptoStream = new CryptoStream(memoryStream, rijKey.CreateDecryptor(),
        CryptoStreamMode.Read);
        byte\[\] pTextBytes = new byte\[encryptedData.Length\];
        int decryptedByteCount = cryptoStream.Read(pTextBytes, 0, pTextBytes.Length);
        memoryStream.Close();
        cryptoStream.Close();
        return pTextBytes;
    }