C# cryptography padding is invalid and cannot be removed

"Padding is invalid and cannot be removed"

public static string encodeAES(string input, string key)
{
	MemoryStream mStream = new MemoryStream();
	AesManaged crypto = new AesManaged();
	CryptoStream cStream = new CryptoStream(mStream, crypto.CreateEncryptor(getEncryptionKey(key, keyLength_AES), crypto.IV), CryptoStreamMode.Write);// getEncryptionKey is defined elsewhere and returns a key formatted for AES based of the user's key
	byte[] toEncrypt = new ASCIIEncoding().GetBytes(input); // TODO
	cStream.Write(toEncrypt, 0, toEncrypt.Length);
	cStream.FlushFinalBlock();
	byte[] ret = mStream.ToArray();
	cStream.Close();
	mStream.Close();
	return new ASCIIEncoding().GetString(ret);
}
public static string decodeAES(string input, string key)
{
	MemoryStream msDecrypt = new MemoryStream(GetBytes(input));
	AesManaged crypto = new AesManaged();
	CryptoStream csDecrypt = new CryptoStream(msDecrypt, crypto.CreateDecryptor(getEncryptionKey(key, keyLength_AES), crypto.IV), CryptoStreamMode.Read);// getEncryptionKey is defined elsewhere and returns a key formatted for AES based of the user's key
	byte[] fromEncrypt = new byte[input.Length];
	csDecrypt.Read(fromEncrypt, 0, fromEncrypt.Length);
	return new ASCIIEncoding().GetString(fromEncrypt);
}