ASP.Net dropdown list - multiple postback - asp.net

Question

I have some inconsistent behaviour with a drop down list.
When it postback and the selected index is 1, it goes through and works as it should, gets the data, builds the UI, and writes everything to the screen.
if the selected index is 2 then it goes through the BuildUI() method, and then goes through the loop again thinking that the selected index is 0 and then doesn't build the UI.
this is the code
Protected Sub Page_Complete() Handles Me.LoadComplete
If _IsAuth = True Then
'if user is authorised to use the application, and the drop down menu has UK or GE
'selected then the the UI will be build for the user.
If Page.IsPostBack And ddlCharterVersion.SelectedIndex > 0 Then
BuildUI()
'once the UI has been built the dropdown list is to be hidden
ScriptManager.RegisterStartupScript(Me, GetType(Page), "ddlCharterVersion", "$('#paymentType').hide();", True)
Else
'if the user is not authorised they are passed a message showing that they are not authorised from the master
'page and the panel holding the divs and information will be hidden
ScriptManager.RegisterStartupScript(Me, GetType(Page), "hidePayments", "$('#panelHead').hide();", True)
End If
End If
End Sub
Protected Sub ddlCharterVersion_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ddlCharterVersion.SelectedIndexChanged
ddlCharterVersion.Enabled = False
End Sub
And this is the dropdown on the page.
<div class="col-md-10 pull-left "><asp:dropdownlist runat="server" width="200px" id="ddlCharterVersion" AutoPostBack="True">
<asp:ListItem Value="-- Select Charter Version -- ">-- Select Charter Version -- </asp:ListItem>
<asp:ListItem Value="UK">UK</asp:ListItem>
<asp:ListItem Value="GE">GE</asp:ListItem>
</asp:dropdownlist></div>
When debugging the application I don't hit any errors that should cause the page to postback.
what puzzles me the most is that selected index position 1 works fine, position 2 does not.
If anyone can see directly what the issue is I would be very grateful for your assistance.
--update--
-- update 2 --
when debugging this, I never hit any of the exceptions, and have a breakpoint on each of them and none of them are ever hit.
Protected Sub BuildUI()
'gets the next record for payment
GetNextRecordForPayment()
If noRecords = False Then
'if there are records, concatenate the list of payments into one row in a list
ConcatenateListOfPayments()
''write the records to the UI
writeRecordsToUI()
End If
End Sub
Protected Sub GetNextRecordForPayment()
Try
''if a user already has a record locked and has refreshed the page for any reason
''get this record back until they pass it to the excptions queue or validate for payment
'UserHasRecordLocked is returned as an object. Either as the contactId of the locked record or False
Dim UserHasRecordLocked = CheckForLockedRecord()
Dim lockedRecord As Long
Dim contactIdParam As New SqlParameter("#LockedRecord", SqlDbType.BigInt)
Dim charterVersionParam As New SqlParameter("#CharterVersion", SqlDbType.VarChar)
charterVersionParam.Value = ddlCharterVersion.SelectedValue
'check the type of object of UserHasRecordLocked
If UserHasRecordLocked.GetType = GetType(Long) Then
'if it has a record then assign the value of UserHasRecordLocked
'to the sqll parameter.
contactIdParam.Value = UserHasRecordLocked
Else
'else give it a default value
contactIdParam.Value = 99999
End If
'place all parameters into a list object of sql parameter
'this has been done this way so that you dont have to be
'precious or careful of where you place your parametss
Dim listOfParam As New List(Of SqlParameter)
listOfParam.Add(contactIdParam)
listOfParam.Add(charterVersionParam)
''gets all records due to be paid
Dim dt As DataTable
'get the first payment \ contact back in a datatable.
'brings back all the parts of the payment, ie redress, d&i, hmrc deductions
'and later concatenates them into one line
dt = DataAccessLayer.FindRecords(listOfParam, _charterPayments, "dbo.usp_getFirstRecordForPayment")
If dt.Rows.Count = 0 Then
noRecords = True
'if there are no records inform the user that there are no payments to be made this day.
ScriptManager.RegisterStartupScript(Me, GetType(Page), "noPayments", "$('#noPayments').modal();", True)
Exit Sub
End If
'build a list of payments using a payee class
BuildListOfPayments(dt)
'using MoreLINQ to get the First or Default record to get the most basic of information out.
Dim paymentInfo = listOfPayments.FirstOrDefault()
''if payment is an IVA, C&R or Deceased Case this will be thrown to the exceptions for manual handling.
If paymentInfo.isException = True Then
'record the exceptions
Dim recorded = RecordNewException(paymentInfo.ContactId, paymentInfo.ContactPartId, paymentInfo.ExceptionReason, True)
If recorded = True Then
'post the page back to get the next record and start the loop again
Response.Redirect(Request.RawUrl, False)
Context.ApplicationInstance.CompleteRequest()
End If
End If
Try
'set the class level variable
_PaymentCategory = paymentInfo.Category
Catch ex As Exception
Dim recorded = RecordNewException(paymentInfo.ContactId, paymentInfo.ContactPartId, "Cannot match complaint against a category type", True)
If recorded = False Then
Response.Redirect(Request.RawUrl, False)
Context.ApplicationInstance.CompleteRequest()
End If
End Try
'lock the record so that no other user can be working on this at the same time
LockRecord(dt)
If paymentInfo.charterVersion = "GE" Then
'if the payment is coming from GE Charter then complete various checks
checkGeCharterPayments(paymentInfo)
ElseIf paymentInfo.charterVersion = "SANUK" Then
'if the payment is coming from GE Charter then complete various checks
checkSanCharterPayments(paymentInfo)
Else
Exit Sub
End If
Catch sqlEx As SqlException
PassToErrorHandler(sqlEx, System.Reflection.MethodInfo.GetCurrentMethod().ToString(), System.Reflection.Assembly.GetExecutingAssembly().GetName().Name)
Catch ex As Exception
PassToErrorHandler(ex, System.Reflection.MethodInfo.GetCurrentMethod().ToString(), System.Reflection.Assembly.GetExecutingAssembly().GetName().Name)
End Try
End Sub