Excel Auto_macro with actxserver problem

Hi,

I have been using actxserver to write to excel for years but now I need to use if to modify a macro enabled .xlsm file and run the macro. I have followed examples on here to run a simple macro but cannot figure out how to use it for my situation.

My .xlsm file has an automatic macro "Workbook_Open" that runs on opening and brings up a userform that requests 4 file locations and a button click. How can I pass these parameters, especially the button click, to the userform and ultimately the macro upon opening? The 4 file locations are also stored in a range in the first worksheet so I can probably modify them with Workbook.Range.Value

I have tried:

    ExcelApp = actxserver('Excel.Application');
    ExcelApp.Visible = 1;
    ExcelFile=ExcelApp.Workbooks.Open(fullfile(pwd,filename));      
    ExcelApp.Run('ThisWorkbook.Workbook_Open','OK_Pressed');

and I have also replaced the last line with:

ExcelApp.Workbooks.Item(Filename).RunAutoMacros(1);

but MATLAB either reports as busy or has errors such as "Invoke Error, Dispatch Exception"

My macro is specified below:

Private Sub Workbook_Open()

   Set DataSheet0 = ThisWorkbook.Worksheets.Item("Sheet1")
   frmProcess.Show
   If (OK_Pressed) Then   'this button click is from the user form "frmProcess"
      Call FREZCONV_Main
   Else
      Call FREZCONV_TidyUp(2)
   End If
    ThisWorkbook.Close

End Sub

Any help with understanding what I'm doing wrong would be greatly appreciated.

John