Are you sure this new file pertains to the problem you are having? I don't see any combobox named "Scheme" or any construct like this
ComboBox("Scheme").List = Worksheets("Validation").Range("A2:A4").Value
or even the word "scheme". The error it produces when I run it, is Runtime error 70 - permission denied. The way to fix that error is to clear the rowsource property before attempting to assign values to list.
Private Sub UserForm_Initialize()
ComboBox1.RowSource = ""
ComboBox1.List = Worksheets("Validation").Range("B2:B88").Value
End Sub