VSTO Excel 2003 to VB 6.0 Type mismatch

Hi,

I have an Addin 2003 Application. In this Application I'm calling an VB 6.0
Dll and I send Excel Application Object as Parameter. In VB Project I'm using
Workbook_Open event with WithEvents. I have a messagebox there. Unfortunately
when i call VB dll , I get this Error Message -- Type mismatch.

Is there any Idea?

Code in VS2008 :
private Project1.Class1 vbapp;

private void ThisAddIn_Startup(object sender, System.EventArgs e)
{
#region VSTO generated code

this.Application =
(Excel.Application)Microsoft.Office.Tools.Excel.Ex celLocale1033Proxy.Wrap(typeof(Excel.Application), this.Application);

#endregion

vbapp = new Class1();
object myAppObject = Globals.ThisAddIn.Application;
try
{
vbapp.AttachApplication(ref myAppObject);
}
catch (Exception ex)
{
}

Code in VB:
Dim WithEvents mExcelApp As Excel.Application

Public Sub AttachApplication(xlApp As Object)
Set mExcelApp = xlApp

End Sub

Private Sub mExcelApp_NewWorkbook(ByVal Wb As Excel.Workbook)
Call MsgBox("New Workbook opened")
End Sub

Private Sub mExcelApp_WorkbookOpen(ByVal Wb As Excel.Workbook)
Call MsgBox("Excel WorkBook opened" + Wb.Name)
End Sub