This works
Function GetValue(path, file, sheet, ref)
'Retrieves a value from a closed workbook
Dim myArg As String
Dim CurrBook As Workbook
'Make sure the file exists
If Right(path, 1) <> "\" Then path = path & "\"
If Dir(path & file) = "" Then
GetValue = "File Not Found"
Exit Function
End If
Application.Workbooks.Open (path & file)
'Create the argument
myArg = "'" & path & "[" & file & "]" & sheet & "'!" & Range(ref).Range("A1").Address(, , xlR1C1)
'Execute an XLM macro
GetValue = ExecuteExcel4Macro(myArg)
Application.Workbooks(file).Close (False)
End Function