vshost32.exe has stopped working either debugging or myproject.exe - vb.net

Question

I'm trying to integrate a scanner to my code, in the sample solution they provided, they use DllImport, Delegate functions, callback procedures, etc...
This is just my first encounter with dllImport, delegates, callback procedures, everytime I debug the solution they gave me, starting from initializing, then button click and then suddenly I always get an error "vshost32.exe has stopped working".
Here's my the code:
Imported Functions from DLL:
Private Declare Function rdInit Lib "sb6lib" (ByVal tmo As Integer) As Integer
Private Declare Function rdStart Lib "sb6lib" () As Integer
Private Declare Function rdsConfig Lib "sb6lib" (ByVal Wnd As Integer, ByVal confile As String) As Integer
Private Declare Function rdConfigAPI Lib "sb6lib" (ByVal tmo As Integer, ByVal tmo As Integer) As Integer
Use of delegates to implement callback procedures.
Public Delegate Sub FeederEmptyDelegate(ByVal x As Integer)
Private Declare Function rdOnFeederEmpty Lib "sb6lib" (ByVal lpfeederempty As FeederEmptyDelegate) As Integer
Public Delegate Sub AllDoneDelegate(ByVal x As Integer)
Private Declare Function rdOnAllDone Lib "sb6lib" (ByVal lpx As AllDoneDelegate) As Integer
Delegate Function CodeLineVBDelegate(ByVal lpx As IntPtr) As Integer
Private Declare Function rdOnCodeLineVB Lib "sb6lib" (ByVal lpx As CodeLineVBDelegate) As Integer
Public Delegate Sub ErrorDelegate(ByVal x As Integer)
Private Declare Function rdOnError Lib "sb6lib" (ByVal lpx As ErrorDelegate) As Integer
Public Delegate Function DocumentDoneDelegate(ByVal lpx As Integer) As Integer
Private Declare Function rdOnDocumentDone Lib "sb6lib" (ByVal lpx As DocumentDoneDelegate) As Integer
On Command1_Click Event -Stands for Initialize Button
Public Sub Command1_Click(ByVal eventSender As System.Object, ByVal eventArgs As System.EventArgs) Handles Command1.Click
Dim rtnval As Object
' find the RDS and initialize the API
rtnval = rdInit(-1)
List1.Items.Add(("rdInit returns " & rtnval))
If rtnval > -1 Then
rtnval = rdConfigAPI(4101, 0)
rtnval = rdsConfig(Frame1.Handle.ToInt32, ".\\DOCDES0.DES")
List1.Items.Add(("rdsConfig returns " & rtnval))
'Callbacks
rtnval = rdOnFeederEmpty(AddressOf feederempty)
rtnval = rdOnAllDone(AddressOf alldone)
rtnval = rdOnCodeLineVB(AddressOf codeline)
rtnval = rdOnError(AddressOf onerror)
rtnval = rdOnDocumentDone(AddressOf docdone)
Command2.Enabled = True
Command1.Enabled = False
Command3.Enabled = True
ViewButton.Enabled = True
End If
End Sub
On Command2_Click Event -Stands for Start Scanning Button
Private Sub Command2_Click(ByVal eventSender As System.Object, ByVal eventArgs As System.EventArgs) Handles Command2.Click
Dim rtnval As Object
rtnval = rdStart()
List1.Items.Add(("rdStart returns " & rtnval))
End Sub
After the scanning (End Sub) it goes to the Callback function "codeline": (Debug Mode)
Private Function codeline(ByVal x As IntPtr) As Integer
' called when a codeline is available
Dim cl As String
cl = System.Runtime.InteropServices.Marshal.PtrToStringBSTR(x) 'conversion necessary as passed argument is a BSTR type string in sb6lib
If Me.InvokeRequired Then
Me.Invoke(New WriteTextBoxDelegate(AddressOf codeline), New Object() {x})
Else
yval.Text = "CL: " & cl
End If
codeline = 1
End Function
and then the application stopped working ("vshost32.exe has stopped working").
Can sombebody tell me what causes the crashing of the application? Thanks!