类型'；System.InvalidOperationException'；发生在System.Web.Ex

为什么这部分代码会出现此错误？

该部分

           var data = serializer.Deserialize<EmailTemplate>(httpRequest.Form["data"].ToString());

我的程序

public int UpdateEmailTemplate()
    {
        HttpResponseMessage result = null;
        ObjectService uploadFile = new ObjectService();
        List<ActiveUp.Net.Mail.Attachment> attachment = new List<ActiveUp.Net.Mail.Attachment>();
        var httpRequest = HttpContext.Current.Request;
        if (httpRequest.Form["data"] != null)
        {
            var serializer = new JavaScriptSerializer();
            var data = serializer.Deserialize<EmailTemplate>(httpRequest.Form["data"].ToString());
            if (httpRequest.Files.Count > 0)
            {
                var docfiles = new List<string>();
                foreach (string file in httpRequest.Files)
                {
                    MemoryStream target = new MemoryStream();
                    httpRequest.Files[file].InputStream.CopyTo(target);
                    uploadFile.AddObject(data.Id, "SU_ENTITY_MSG_TEMPLATE","", target.GetBuffer(), httpRequest.Files[file].FileName);
                }
            }
            AdminService List = new AdminService();
            return List.UpdateEmailTemplate(data);
    }

我的

public class EmailTemplate
{
   public int Id;
   public string TypeObject;
   public int? idObject;
   public string ObjectName;
   public string IdTeam;
   public string IdTask;
   public string Team;
   public string task;
   public string Title;
   public string Subject;
   public string dataHtml;
   public List<Objects> fileListRequest;
}

httpRequest.Form["data"]