i have more checkboxes in 1 row and about 5 columns in a gridview, i need to get a value for each, can someone help please

i have more checkboxes in 1 row and about 5 columns in a gridview, i need to get a value for each, can someone help please!!!
this is what i have tried but it gives the following error
"system.Web.UI.LiteralControl' to type 'Excel.CheckBox'"
 
For index As Integer = 0 To Me.GridView1.Rows.Count - 1
Dim row As GridViewRow = Me.GridView1.Rows(index)
For i As Integer = 4 To row.Cells.Count - 1 
 Dim cb As CheckBox = CType(GridView1.Rows(index).Cells(i).FindControl("Present"), CheckBox)
 If cb IsNot Nothing Then
 If cb.Checked = True Then
code here.......
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