ArgumentOutOfRangeException when trying to clear combobox - vb.net

Question

I'm having the following error message appear when trying to run .Clear() on my combobox:
A first chance exception of type 'System.ArgumentOutOfRangeException' occurred in System.Windows.Forms.dll
{"InvalidArgument=Value of '-1' is not valid for 'index'.
Parameter name: index"}
The strange part is, it does the .Clear() before going to the new 'page' in the application, and it works without a problem. Once I'm on the 'page', draw the items in the combobox and try to go to the next 'page' of the application, it calls the function with the clear once again and blows up when it gets to the .Clear(). If I comment out the cbo.DrawMode = DrawMode.OwnerDrawFixed in the code below it also runs as normal, so the problem is definitely with drawing the strings in the combobox (I'm drawing the strings to change the colour of them). Anyways, completely stumped as to how to fix this, any help would be appreciated.
Code is below:
-My clear method
Public Sub ClearCombos()
'Clear Applicant Combos
cboPrimary.Items.Clear() 'crashes when it hits this line
cboJoin1.Items.Clear()
cboJoin2.Items.Clear()
cboJoin3.Items.Clear()
cboJoin4.Items.Clear()
End Sub
Drawing the strings in the comboboxes
Sub CheckForAgeOverage()
c_applicants = {cboPrimary, cboJoin1, cboJoin2, cboJoin3, cboJoin4}
Dim curdate As Date = Date.Now
Dim age As Integer
counter = 0
'Check age of applicants
For Each cbo As ComboBox In c_applicants
If CKeyValuePair.GetComboBoxSelectedKey(c_applicants(counter), True) = instApplicant.applicantId Then
age = Math.Floor(DateDiff(DateInterval.Month, DateValue(instApplicant.BirthDate), curdate) / 12)
If age >= 70 Then
overArray.Add(CKeyValuePair.GetComboBoxSelectedValue(c_applicants(counter)))
End If
cbo.DrawMode = DrawMode.OwnerDrawFixed
Else
For Each j As JoinsBU In instJoins
If CKeyValuePair.GetComboBoxSelectedKey(c_applicants(counter), True) = j.Applicant.applicantId Then
age = Math.Floor(DateDiff(DateInterval.Month, DateValue(j.Applicant.BirthDate), curdate) / 12)
If age >= 70 Then
overArray.Add(CKeyValuePair.GetComboBoxSelectedValue(c_applicants(counter)))
End If
cbo.DrawMode = DrawMode.OwnerDrawFixed
End If
Next
End If
counter += 1
Next
End Sub
The Comboboxes DrawItem event:
Private Sub cbo_DrawItem(sender As System.Object, e As System.Windows.Forms.DrawItemEventArgs) Handles cboPrimary.DrawItem, cboJoin1.DrawItem, cboJoin2.DrawItem, cboJoin3.DrawItem, cboJoin4.DrawItem
Dim brush As Brush = Brushes.Black
Dim text As String = (CType(sender, ComboBox)).Items(e.Index).ToString()
counter = 0
For Each s As String In overArray
If text = overArray(counter) Then
brush = Brushes.Red
Else
brush = Brushes.Black
End If
counter += 1
Next
e.Graphics.DrawString(sender.Items(e.Index).ToString(), e.Font, brush, _
e.Bounds, StringFormat.GenericDefault)
counter = 0
End Sub

Answer 1

It looks like this shouldn't happen, but it obviously is. The actual error might be in this line in the DrawItem handler:
Dim text As String = (CType(sender, ComboBox)).Items(e.Index).ToString()
Try separating the assignment out of the Dim statement, and check the value of e.Index to make sure it is non-negative. If that's the problem, you could probably work around it with an if to make sure e.Index is non-negative.