VB.net Nested Structures

See more:

VB

First of all, this is my first post here so I hope I post this correctly. I've used this site many times to find answers to other issues but I have never had to post a question before.

I have a VB.net program that I use to communicate with a Fanuc CNC controller with a PC front end using the Fanuc Focas Libraries. The Fanuc CNC controller controls the operation of a machine tool that is used to cut metal parts. The Fanuc controller has a series of macro variables used to store numeric values. I am currently able to call different Fanuc functions to read and write a single variable at a time.
My VB.net program currently reads several macro variables at a time via a timer so I am would like to limit the number of calls I make to the Fanuc. I noticed that the Fanuc also offers another function that can be used to either read or write a series of variables at once. I have been trying to get this function to work but I have not been having any luck.

The documentation I got from Fanuc has an example in it but it looks like its written in C++. I called tech support at Fanuc and they provided me with some VB examples files that look like they were written in code prior to VB6
Based on all this information, I created the following code. The structure the FANUC uses for this function has a nested structure and I have never done one of those before. I have tried writing the nested structure 2 ways. The C++ example I have showed the nested structure defined within the primary structure. The VB3 example showed the nested structure as its own structure that gets called by the primary structure. Both way didn't work. I think this where I'm having my issue because the other functions that I used to read/write single variables are not nested. The following is an example of the code I'm using:

Structures:

<StructLayout(LayoutKind.Sequential, Pack:=4)> _
    Public Structure IODBMR
        Public datano_s As Short  ' start macro number 
        Public dummy As Short     ' dummy 
        Public datano_e As Short  ' end macro number 
        Public data() As IODBMR_data ' data
    End Structure
   
 <StructLayout(LayoutKind.Sequential,Pack:=4)> _
    Public Structure IODBMR_data
        Public mcr_val As Integer ' macro variable 
        Public dec_val As Short   ' decimal point 
    End Structure

Function Call:

' read custom macro variables(area specified)
   Declare Function cnc_rdmacror Lib "FWLIB32.DLL" _
       ( ByVal FlibHndl As Integer, ByVal a As Short, ByVal b As Short, ByVal c As Short, ByRef d As IODBMR ) As Short

Code to read 5 variables at once:

Private Sub BtnReadMacroRange_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnReadMacroRange.Click
        'Read a series of 5 variables from the Fanuc
        'StartVar = start macro variable number which is input via the GUI
        'End Var = ending macro variable number which is input via the GUI
        'Length = length of structure which is input via the GUI
        Try
            Dim StartVar As Integer = CInt(Me.TxtStartVar.Text)
            Dim EndVar As Integer = CInt(Me.TxtEndVar.Text)
            Dim Length As Integer
            Dim McrVal As Integer
            Dim DecVal As Integer
            Dim VariableNumber As Integer
            Dim Result As String = Nothing
            Dim MacroRange As New Focas1.IODBMR
            Length = CInt(Me.TxtReadMacroRangeLength.Text)

            'Call the Fanuc Function
            'FlibHndl needs to be obtained first
            nRet = Focas1.cnc_rdmacror(FlibHndl, StartVar, EndVar, Length, MacroRange)
            'MsgBox("FlibHndl = " & FlibHndl)
            TextBox1.Text = CStr(nRet)
            'Read the result of a single variable and write the info to the GUI
            For x As Integer = 0 To 4
                VariableNumber = StartVar + x
                McrVal = MacroRange.data(x).mcr_val
                DecVal = MacroRange.data(x).dec_val
                If McrVal = 0 And DecVal = -1 Then
                    Result = "Null"
                Else
                    Result = McrVal * 10 ^ -(DecVal)
                End If

                Select Case x
                    Case 0
                        Me.LblReadMacroRangeResult1.Text = VariableNumber
                        Me.TxtReadMacroRangeResult1.Text = Result
                    Case 1
                        Me.LblReadMacroRangeResult2.Text = VariableNumber
                        Me.TxtReadMacroRangeResult2.Text = Result
                    Case 2
                        Me.LblReadMacroRangeResult3.Text = VariableNumber
                        Me.TxtReadMacroRangeResult3.Text = Result
                    Case 3
                        Me.LblReadMacroRangeResult4.Text = VariableNumber
                        Me.TxtReadMacroRangeResult4.Text = Result
                    Case 4
                        Me.LblReadMacroRangeResult5.Text = VariableNumber
                        Me.TxtReadMacroRangeResult5.Text = Result
                End Select
            Next
        Catch ex As Exception
            MsgBox(ex.Message.ToString)
        End Try
    End Sub

When I try to run this code, the whole application crashes and gives me the dreaded "Sorry for the inconvience error" despite having the code wrapped in try/catch. I've been working with the techs at Fanuc but they don't seem to have many people that know a lot about VB.net. Can anyone find anything that I'm doing wrong?

Thanks,