Retrieve and Update Files

The first lines in Private Sub Retrieve_Click() macro should be

Dim Rowcount2 As Long
    Rowcount2 = Sheet1.Range("A1").Value

It's always good practice to Dim Variables first, and refer to sheets with their VBA code name not tab name

Your code would have worked had you used

Rowcount2 = Sheets("Form").Range("A1").Value

but as I said use the sheet codename, the tab name is too easily changed by the user and a macro that uses it will fall over.