vba excel If condition error on final iteration - vba

Question

I'm having the code takes the input from my checkboxes and grab data from the related worksheet. I ran it line by line and found out that it always gets a runtime error at the If statement on the final loop. Is there something wrong in my code?
Option Explicit
Private Sub UserForm_Initialize()
Dim counter As Long
Dim chkBox As MSForms.CheckBox
''''Add checkboxes based on total sheet count
For counter = 1 To Sheets.count - 2
Set chkBox = Me.Frame1.Controls.Add("Forms.CheckBox.1", "CheckBox" & counter)
chkBox.Caption = Sheets(counter + 2).Name
chkBox.Left = 10
chkBox.Top = 5 + ((counter - 1) * 20)
Next
End Sub
Private Sub cmdContinue_Click()
Dim Series As Object
Dim counter As Long
'''Clear old series
For Each Series In Sheets(2).SeriesCollection
Sheets(2).SeriesCollection(1).Delete
Next
''Cycle through checkboxes
For counter = 1 To Sheets.count - 2
''If the box is checked then
If Me.Frame1.Controls(counter).Value = True Then ''Error here on 4th iteration
''Add new series
With Sheets(2).SeriesCollection.NewSeries
.Name = Sheets(counter + 2).Range("$A$1")
.XValues = Sheets(counter + 2).Range("$A$12:$A$25")
.Values = Sheets(counter + 2).Range("$B$12:$B$25")
End With
End If
Next counter
Me.Hide
End Sub
Also, a second problem is it always run on the wrong loop. If i check box 2 it'll run data for the box 1 sheet, 3 run for 2, 4 run for 3, and 1 run for 4. Can anyone explain the reason behind this?
EDIT: So as VincentG point out below, adding an explicit name "checkbox" in there did the trick (i didn't know you could do that). Index 1 was probably taken by one of the buttons or the frame in the user form, causing it to get off set.

Answer 1

I guess your main problem comes from the fact that the controls have to be accessed starting from index 0. So to loop over all controls, you would do something like
For counter = 0 To Me.Frame1.Controls.Count - 1
Debug.Print counter; Me.Frame1.Controls(counter).Name
Next counter
So, when you stick to you code, I assume you have to change the if-statement to
If Me.Frame1.Controls(counter-1).Value = True Then