Selecting Non Sequenced Cells In A Range

I'm trying to use the SUM function with non sequenced cell but the Range or any other function won't allow me to activate the selecting cells if there are more then 41 cell, I wrote somthing like so:


Sub Test()
Dim str AS String
Dim R AS Range

str = "A1,A3 ...... ,A57" 'this is only an example, assum that there are _
more then 41 cells
Set R = Range(str) 'Here is the Problem, I get a Runtime error 1004 _
Application-defined or object-defined error
R.select
End Sub

But if the str input was a 41 or less Cells address string then it works