无法访问已关闭的文件错误

尝试反序列化到XML时，我得到错误"无法访问关闭的文件"。我有一个加密的文件。当我得到这个错误时，我解密文件并尝试反序列化它。没有加密和解密也能正常工作。

XmlSerializer xmlSerializer = new XmlSerializer(typeof(Models.Test));
var fileLocStream = FileManipultions.DecryptToStream(fileLoc);
var testResult = (Models.Test)xmlSerializer.Deserialize(FileManipultions.DecryptToStream(fileLoc));

 public static Stream DecryptToStream(string inputFilePath)
        {
            try
            {
                string EncryptionKey = ConfigurationManager.AppSettings["EncDesKey"].ToString();
                CryptoStream cs;
                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 (FileStream fsInput = new FileStream(inputFilePath, FileMode.Open))
                    {
                        cs = new CryptoStream(fsInput, encryptor.CreateDecryptor(), CryptoStreamMode.Read);
                    }
                }
                return cs;
            }
            catch (Exception ex)
            {
                Logger.LogException(ex.Message, System.Reflection.MethodBase.GetCurrentMethod().ToString());
                return null;
            }
        }