Pass ListBox to Function as argument not working - type mismatch when calling function

Hi, 

I am trying to pass a ListBox to a function as an argument but when calling the function I get a mismatch on the name of the ListBox, I have put the code below.

```

Function listAvailableFiles(FolderPath As String, DropDown As ListBox)

    Dim File As String
    Dim j As Integer
    File = Dir(FolderPath & "\*.cdr")
    Do While File <> ""
        DropDown.AddItem File
        File = Dir
    Loop

End Function

Private Sub UserForm_Activate()
    Dim DimensionFolder As String
    DimensionFolder = "C:\Users\cwats\OneDrive - Watson Memorials\Watson Memorials\Designs Template and Drawings\MD UK\Memorial Shapes\Foundations"
    Call listAvailableFiles(DimensionFolder, ListDimensionFilesDropdown)
End Sub
```

Any help on this will be greatly appreciated, I've been googling it for 2 hours 

TIA