ASP.NET

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?

In a vb.net 2010 web form application, I have the start of code for a master page listed below:

#Region "Private Sub Page_Load(ByVal sender As System.Object, ByVal e As 
System.EventArgs) Handles MyBase.Load" 
    Private Sub Page_Load(ByVal sender As System.Object, ByVal e As 
System.EventArgs) Handles MyBase.Load 
 
        _master = CType(Page.Master, MasterPage) 
        _master.PageTitle = "Attendance" 

In the master page, there is an area to display error messages. When I have decided to place an
error message in the master page, I have made a call to a (static) shared function from an ajax call
to obtain data from the sql server database. The ajax call is made from a javascript function.

Thus can you tell me if there is away that I can access the error section of the of the master page?
Basically I need to have the master page with scope to access.
Thus can you tell me if this is possbile and/or show me the code on how to solve my problem?

I am having a problem with an ajax call to a shared (static) vb.net function to obtain data from the database.
In a vb.net 2010 web form application, I needed to make a call from a javascript function to a shared (static) function to
obtain data from a sql server 2012 database. The first ajax call below is the original call and the second call is the one
I came up by copying the first call.
The problem is the first call always occurs before the second ajax call regardless of what I do with the code. There are cases when I
only want the second call to occur. By stepping through the code, I see that there is alot of jquery code that occurs.
$.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                 
            }               
        } 

Thus would you tell me what you think is wrong and/or tell me how I can change the second ajax call to try to solve this issue?   

<asp:TemplateField HeaderText="Student Name" ItemStyle-HorizontalAlign="Center" 
ItemStyle-CssClass="ui-widget-content" > 
                                <ItemTemplate > 
                                    <a href="javascript: 
GetStudentLetterTemplate('<%# Eval("schoolyear") %>', '<%# Eval("schoolnum") 
%>', '<%# Eval("milestone_code") %>', '<%# Eval("stulink") %>', '<%# 
Eval("HOMELNGCOR") %>', '<%# Eval("semester") %>');" 
style="color:Blue"><%#Eval("STUDENTNAME")%></a> 
                                </ItemTemplate> 
                            </asp:TemplateField> 

 #Region "Public Shared Function GetDupScoolYear"
<WebMethod()> _
Public Shared Function GetDupScoolYear() As DataTable
    Dim _dt As DataTable = New DataTable()

    Dim Query As String = "SELECT [personID],value, count(*) as Count FROM
   [t].[dbo].[CustomStudent] where attributeID = 2775 and [personID] = 97366 group
   by [personID],value"
    Using con As SqlConnection = DB.OpenConnection()
        Using da As SqlDataAdapter = New SqlDataAdapter(Query, con)

            Try
                da.Fill(_dt)
            Catch ex As Exception

            End Try

        End Using
        End Using
       Return _dt
     End Function
   #End Region