[vba] Excel Validation Drop Down list using VBA

You are defining your array as xlValidateList(), so when you try to assign the type, it gets confused as to what you are trying to assign to the type.

Instead, try this:

Dim MyList(5) As String
MyList(0) = 1
MyList(1) = 2
MyList(2) = 3
MyList(3) = 4
MyList(4) = 5
MyList(5) = 6

With Range("A1").Validation
    .Delete
    .Add Type:=xlValidateList, AlertStyle:=xlValidAlertStop, _
         Operator:=xlBetween, Formula1:=Join(MyList, ",")
End With