Težava z array v Visual Basic

zanima me, zakaj v naslednji kodi ne morem uporabiti ubound:

Dim kombinacija(t - 1) As String
kombinacija(t - 1) = CStr(CheckedListBox1.CheckedItems(t - 1))

If kombinacija(t - 1) = "2106-1227" Then

Dim x(0 To 6), y(0 To 6) As Double

y(0) = 455271
x(0) = 123544
y(1) = 455375
x(1) = 123556
y(2) = 455378
x(2) = 123545
y(3) = 455381
x(3) = 123502
y(4) = 455310
x(4) = 123502
y(5) = 455295
x(5) = 123504
y(6) = 455272
x(6) = 123504


ElseIf kombinacija(t - 1) = "2106-1228" Then

Dim x(0 To 3), y(0 To 3) As Double

y(0) = 455272
x(0) = 123551
y(1) = 455271
x(1) = 123544
y(2) = 455272
x(2) = 123504
y(3) = 455202
x(3) = 123513

ElseIf kombinacija(t - 1) = "2119-543" Then


Dim x(0 To 9), y(0 To 9) As Double

y(0) = 455381
x(0) = 123495
y(1) = 455306
x(1) = 123494
y(2) = 455299
x(2) = 123494
y(3) = 455205
x(3) = 123494
y(4) = 455194
x(4) = 123509
y(5) = 455202
x(5) = 123513
y(6) = 455272
x(6) = 123504
y(7) = 455295
x(7) = 123504
y(8) = 455310
x(8) = 123502
y(9) = 455381
x(9) = 123502


End If

Dim i As Integer
Dim sum1 As Double = 0
Dim sum2 As Double = 0

For i = 0 To UBound(Y)