Dim sSplitString As String = "12ab45de78gh"
Dim iLaenge As Integer = 2
Dim arErgebnis() As String
arErgebnis = (Enumerable.Range(0, sSplitString.Length / iLaenge).Select( _
  Function(x) sSplitString.Substring(x * iLaenge, iLaenge)).ToArray())
System.Array.Reverse(arErgebnis)
For Each sWert As String In arErgebnis
    MsgBox(sWert)
Next