ASP.NET

public class COMProjectNameValidator:IValidator
 {

      MessageInfo _MessageInfo = new MessageInfo();
      public void Validate(object obj, MessageList MessageList)
      {
           COMProjectDTO _COMProjectDTO=(COMProjectDTO)obj;
           if (DAOUtil.IsValuePersisted(typeof(COMProjectEntity), "Id", _COMProjectDTO.COMProjectId) == false)
           {
               IGenericExtnDAO<COMProjectEntity> IGenericExtnCOMProjectLoadDAO = DAOFactory.Instance.GetGenericDAO<COMProjectEntity>();
               List<COMProjectEntity> _COMProjectEntityList = IGenericExtnCOMProjectLoadDAO.FindAll().Where(t => t.COMBranch!= null && t.COMBranch.Id == _COMProjectDTO.COMBranchId).ToList();

//if (_COMProjectEntityList.Select(t => t.ProjectName).ToList().Contains(_COMProjectDTO.ProjectName))
                //{
                //    MessageInfo _MessageInfo = new MessageInfo(KEYS.COM_Project_Name_ALREADY_EXIST, AlertMessageTypeEnum.Error);
                //    MessageList.Add(_MessageInfo);
                //}
            }
            else
            {
                IGenericExtnDAO<COMProjectEntity> IGenericExtnCOMProjectLoadDAO = DAOFactory.Instance.GetGenericDAO<COMProjectEntity>();
                COMProjectEntity _COMProjectEntity = IGenericExtnCOMProjectLoadDAO.Get(_COMProjectDTO.COMProjectId);
                if (_COMProjectEntity.ProjectName != _COMProjectDTO.ProjectName)
                {
                    IGenericExtnDAO<COMProjectEntity> IGenericExtnCOMProjectLoadDAOForExist = DAOFactory.Instance.GetGenericDAO<COMProjectEntity>();
                    List<COMProjectEntity> _COMProjectEntityList = IGenericExtnCOMProjectLoadDAO.FindAll().Where(t => t.COMBranch!= null && t.COMBranch.Id == _COMProjectDTO.COMBranchId).ToList();
                    if (_COMProjectEntityList.Select(t => t.ProjectName).ToList().Contains(_COMProjectDTO.ProjectName))
                    {
                        MessageInfo _MessageInfo = new MessageInfo(KEYS.COM_Project_Name_ALREADY_EXIST, AlertMessageTypeEnum.Error);
                        MessageList.Add(_MessageInfo);
                    }
                }

            }
           }

       }

In 2 ajax calls that are listed below, there are 2 places that say 'error: AjaxFailed'.  

$.ajax({ 
                    type: "POST", 
                    contentType: "application/json; charset=utf-8", 
                    url: document.location.pathname + "/GetStudentLetter", 
                    data: "{ " + strData + " }", 
                    dataType: "json", 
                    success: function (data) { 
                        LoadEditor(JSON.parse(data.d), milestone); 
                    }, 
                    error: AjaxFailed 
                });            
            if (milestone == '999') { 
                $.ajax({ 
                    type: "POST", 
                    contentType: "application/json; charset=utf-8", 
                    url: document.location.pathname + "/Gettattschyr", 
                    data: "{ " + strData + " }", 
                    dataType: "json", 
                    success: function (data) { 
                        successtest(eval(data));                       
                    }, 
                    error: AjaxFailed 
                }); 
            }                
         }           
        function successtest(sletter) { 
            var sle = sletter 
            _txtattschyr = sletter.d 
            if (_txtattschyr > '1') { 
                alert('You have selected student(s) having more than one Entry for the current school year. '); 
                return                 
            }               
I would like to have better error handling so that I know what is exactly wrong. From the first ajax call, I got a 500 server error problem 
in production. By guessing, I found out that I needed to increase the maximum size of the jason file that is posted above.

Thus can you tell and/or point me to urls that will show me better error logic that I can use?