Updating DataTable inside as DataSet - datatable

Question

In an accounting WPF app we have a number of public DataTables that reload data once a tab is opened. This works great locally as the reports just refer to those tables..
For some more complex reports we have just set up a Web Service to run them and return a PDF... To make it easier I thought of loading these DataTables into a DataSet and then extracting them at the server end. This works perfectly the first time it's run, but then (as best as I can work out so far) it's sending the incorrect (last loaded) data for subsequent reports. Locally it still works as it should but the DataTables we are sending in the DataSet appear to not be updating. Have tried to remove the tables and re-add them again, but that just throws a 'object reference not set' the first time a DataRow is selected from a DataTable at the server.
Must be something very basic I have been missing :-(
Any ideas?
Thanks
Private Async Sub RunProfitAndLossOnServer(sender As Object, e As RoutedEventArgs)
Try
Dim StartDateTB As DateTBx = ReportBalanceSheet_Grid.FindName("BalanceSheet_StartDateTB")
Dim EndDateTB As DateTBx = ReportBalanceSheet_Grid.FindName("BalanceSheet_EndDateTB")
ReportStartDate = StartDateTB.Value
ReportEndDate = EndDateTB.Value
ReportDate = Today
ReportName = "Profit and Loss Report"
PaperLandscape = False
ReportFontSize = 8
PopupModals_ReportGenerator()
If ReportGeneratorRun = True Then
Dim vPDF() As Byte = Nothing
'Determine if the Export Dataset has already been created
If ExportDS Is Nothing Then
ExportDS = New DataSet
VariablesDT = New DataTable
With VariablesDT.Columns
.Add("Current_HOA_Name", GetType(String))
.Add("Current_HOA_ID", GetType(Integer))
.Add("ReportName", GetType(String))
.Add("ReportFontSize", GetType(Integer))
.Add("ReportStartDate", GetType(Date))
.Add("ReportEndDate", GetType(Date))
.Add("User_InternationalDate", GetType(Integer))
.Add("PaperSize", GetType(String))
.Add("PaperLandscape", GetType(Boolean))
.Add("Reports_IsSplitGL", GetType(Boolean))
.Add("Form_ID", GetType(Integer))
End With
With VariablesDT.Rows
.Add(Current_HOA_Name, Current_HOA_ID, ReportName, ReportFontSize, ReportStartDate, ReportEndDate, User_InternationalDate, PaperSize, PaperLandscape, False, Form_ID)
End With
VariablesDT.TableName = "VariablesDT"
ExportDS.Tables.Add(VariablesDT)
ResIncomeDT.TableName = "ResIncomeDT"
ExportDS.Tables.Add(ResIncomeDT)
ResIncNomDT.TableName = "ResIncNomDT"
ExportDS.Tables.Add(ResIncNomDT)
ResExpensesDT.TableName = "ResExpensesDT"
ExportDS.Tables.Add(ResExpensesDT)
ResExpNomDT.TableName = "ResExpNomDT"
ExportDS.Tables.Add(ResExpNomDT)
RevenueDT.TableName = "RevenueDT"
ExportDS.Tables.Add(RevenueDT)
ExpensesDT.TableName = "ExpensesDT"
ExportDS.Tables.Add(ExpensesDT)
RevenueNomDT.TableName = "RevenueNomDT"
ExportDS.Tables.Add(RevenueNomDT)
ExpensesNomDT.TableName = "ExpensesNomDT"
ExportDS.Tables.Add(ExpensesNomDT)
Else
ExportDS.Tables.Remove("ResIncomeDT")
ExportDS.Tables.Remove("ResIncNomDT")
ExportDS.Tables.Remove("ResExpensesDT")
ExportDS.Tables.Remove("ResExpNomDT")
ExportDS.Tables.Remove("RevenueDT")
ExportDS.Tables.Remove("ExpensesDT")
ExportDS.Tables.Remove("RevenueNomDT")
ExportDS.Tables.Remove("ExpensesNomDT")
ExportDS.Tables.Add(ResIncomeDT)
ExportDS.Tables.Add(ResIncNomDT)
ExportDS.Tables.Add(ResExpensesDT)
ExportDS.Tables.Add(ResExpNomDT)
ExportDS.Tables.Add(RevenueDT)
ExportDS.Tables.Add(ExpensesDT)
ExportDS.Tables.Add(RevenueNomDT)
ExportDS.Tables.Add(ExpensesNomDT)
ExportDS.Tables.Remove("VariablesDT")
For Each row As DataRow In VariablesDT.Rows
row("Current_HOA_Name") = Current_HOA_Name
row("current_HOA_ID") = Current_HOA_ID
row("ReportFontSize") = ReportFontSize
row("User_InternationalDate") = User_InternationalDate
row("PaperSize") = PaperSize
row("PaperLandscape") = PaperLandscape
row("Reports_IsSplitGL") = False
row("ReportStartDate") = ReportStartDate
row("ReportEndDate") = ReportEndDate
row("ReportName") = ReportName
row("Form_ID") = Form_ID
Next
ExportDS.Tables.Add(VariablesDT)
End If
Dim vImage As New LoadingImage
LoadingStarted("Uploading to xSoftware... Please wait...", vImage)
Await Task.Run(Sub()
Using vService As New Service5Client
vPDF = vService.ReturnProfitAndLossSheet(ExportDS)
End Using
End Sub)
LoadingCompleted("File uploaded to xSoftware...", "File was uploaded and PDF returned...", vImage)
Dim vFile As String = ByteToFilePath(vPDF)
If System.IO.File.Exists(vFile) Then
Dim P As New Process
With P
.StartInfo.FileName = vFile
.StartInfo.Verb = "Open"
.Start()
End With
Else
AppBoxError("The file path for the PDF is not valid!")
End If
End If
Catch ex As Exception
EmailError(ex)
End Try
End Sub
Throws an error at the server end if we remove and add the datatables back to the DataSet
Dim RevenueData() As DataRow = RevenueDT.Select("FormID = " & Form_ID, "Position")
Dim ExpenseData() As DataRow = ExpensesDT.Select("FormID = " & Form_ID, "Position")
Dim RevenueNomData() As DataRow = RevenueNomDT.Select("FormID = " & Form_ID, "Position")
Dim ExpenseNomData() As DataRow = ExpensesNomDT.Select("FormID = " & Form_ID, "Position")

Answer 1

It looks like the answer is
Remove the DataTables from the DataSet and add them again (which got us part of the way there)
Name the DataTables again!
ExportDS.Tables.Remove("ResIncomeDT")
ExportDS.Tables.Remove("ResIncNomDT")
ExportDS.Tables.Remove("ResExpensesDT")
ExportDS.Tables.Remove("ResExpNomDT")
ExportDS.Tables.Remove("RevenueDT")
ExportDS.Tables.Remove("ExpensesDT")
ExportDS.Tables.Remove("RevenueNomDT")
ExportDS.Tables.Remove("ExpensesNomDT")
ExportDS.Tables.Remove("VariablesDT")
VariablesDT.TableName = "VariablesDT"
ExportDS.Tables.Add(VariablesDT)
ResIncomeDT.TableName = "ResIncomeDT"
ExportDS.Tables.Add(ResIncomeDT)
ResIncNomDT.TableName = "ResIncNomDT"
ExportDS.Tables.Add(ResIncNomDT)
ResExpensesDT.TableName = "ResExpensesDT"
ExportDS.Tables.Add(ResExpensesDT)
ResExpNomDT.TableName = "ResExpNomDT"
ExportDS.Tables.Add(ResExpNomDT)
RevenueDT.TableName = "RevenueDT"
ExportDS.Tables.Add(RevenueDT)
ExpensesDT.TableName = "ExpensesDT"
ExportDS.Tables.Add(ExpensesDT)
RevenueNomDT.TableName = "RevenueNomDT"
ExportDS.Tables.Add(RevenueNomDT)
ExpensesNomDT.TableName = "ExpensesNomDT"
ExportDS.Tables.Add(ExpensesNomDT)
Now it appears to be working correctly :-)