having an Issue with my dynamically built checkboxes on gridview

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C#

Gridview

ok, I having an issue when I am trying to collect the checkbox values for dynamically built gridview, it is saying index not found.

public List<string> GetSignsPrinted()
    {
        List<string> selectedIds = new List<string>();

        DataColumn printedColumn = SourceTable.Columns["Column_PRINT"];

        if (printedColumn != null)
        {
            foreach (GridViewRow row in this.GridView1.Rows)
            {
                CheckBox cbPrint = row.Cells[printedColumn.Ordinal].Controls[0] as CheckBox;
                if (cbPrint is CheckBox)
                {
                    if (cbPrint.Checked)
                    {
                        selectedIds.Add(cbPrint.ID);
                    }
                }
            }
        }
        return selectedIds;
    }

Any Help appreciated!