VB.NET - Error on Export to Excel

Imports System.Data
Imports System.Reflection
Imports ClosedXML.Excel

Private Sub Button4_Click_1(sender As Object, e As EventArgs) Handles btnExportToExcel.Click
        'Creating DataTable
        Dim dt As New DataTable()

        'Adding the Columns
        For Each column As DataGridViewColumn In DataGridView1.Columns
            dt.Columns.Add(column.HeaderText, column.ValueType)
        Next

        'Adding the Rows
        For Each row As DataGridViewRow In DataGridView1.Rows
            dt.Rows.Add()
            For Each cell As DataGridViewCell In row.Cells
                dt.Rows(dt.Rows.Count - 1)(cell.ColumnIndex) = cell.Value.ToString()
            Next
        Next

        'Exporting to Excel
        Dim folderPath As String = "C:\"
        If Not Directory.Exists(folderPath) Then
            Directory.CreateDirectory(folderPath)
        End If
        Using wb As New XLWorkbook()
            wb.Worksheets.Add(dt, "Customers")
            wb.SaveAs(folderPath & Convert.ToString("DataGridViewExport.xlsx"))
        End Using
    End Sub