How to allow users to only check one checkbox in a datagrid view

Hi all,

I am working on a project affiliated to customer's database and i am required to insert, update, delete the data through a window's form program. The database i am using is MS SQL server 2005 and one of the columns i had is "Selection" which its datatype is set to "bits" which is used as a checkbox control in the datagridview in my program.  The checkbox allows me to choose the specific row of customer's data, which i append to textboxes, but there is one problem, i am able to multiple-select the checkboxes. I want to restrict the datagridview checkbox column to only be able to select only one checkbox/one row at a time. The follow is part of the codes I've done so far:-

Any help would be greatly appreciated.
Thank you.

Imports System.Data
Imports System.Data.SqlClient
Imports System.Threading
Imports System.Text.RegularExpressions
Imports System.Text

Public Class Form3


    Dim da As SqlDataAdapter
    Dim conn As SqlConnection
    Dim bsource As BindingSource = New BindingSource()
    Dim ds As DataSet
    Dim firstname As String
    Dim sql As String
    Dim pnum As String
    Dim msg As String
    Dim MaxRows As Integer
    Dim i As Integer



    Private Sub Form3_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        btnUpdate.Visible = False

        Dim myCommand As New SqlCommand(sql, conn)


        Dim connectionString As String = "Data Source=ITCU-23\SQLEXPRESS;Initial Catalog=compare;" & "Integrated Security=SSPI;"
        conn = New SqlConnection(connectionString)

        sql = "SELECT * FROM  Alarms"


        da = New SqlDataAdapter(sql, conn)
        ds = New DataSet()
        Dim commandBuilder As SqlCommandBuilder = New SqlCommandBuilder(da)
        da.Fill(ds, "Alarms")
        DataGridView1.DataSource = ds.Tables("Alarms")


        MaxRows = ds.Tables("Alarms").Rows.Count
        MaxRows = MaxRows - 1
        ' MsgBox(ds.Tables("Alarms").Rows(MaxRows).Item(0))

        btnEdit.Enabled = False
        btnDel.Enabled = False

        Dim i As Integer
        Dim dr As DataTable = CType(DataGridView1.DataSource, DataTable)
        For i = 0 To (dr.Rows.Count - 1)

            DataGridView1.Rows(i).Cells("Selection").Value = DBNull.Value

        Next i


        'MsgBox(ds.Tables("Alarms").Rows(MaxRows).Item(0))

    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnInsert.Click

        Dim name As String = txtName.Text

        Dim blk As String = txtBlock.Text

        Dim eNo As String = txtNum.Text

        Dim unit As String = txtUnit.Text

        Dim dsNewRow As DataRow

        dsNewRow = ds.Tables("Alarms").NewRow()

        dsNewRow.Item("CustID") = ds.Tables("Alarms").Rows(MaxRows).Item(0) + 1

        Dim signal As String = "Unit " & ds.Tables("Alarms").Rows(MaxRows).Item(0) + 1 & " on fire"
        dsNewRow.Item("Signal") = signal

        If (String.IsNullOrEmpty(name) Or IsNumeric(name) = True) Then

            MsgBox("Please enter a proper name")
            Exit Sub

        End If

        If (String.IsNullOrEmpty(blk) = True) Then
            MsgBox("Please enter Block Name")
            Exit Sub

        End If

        If (String.IsNullOrEmpty(unit) = True) Then
            MsgBox("Please enter a proper unit number")
            Exit Sub

        End If

        If (IsNumeric(eNo) = False Or String.IsNullOrEmpty(eNo)) Then

            MsgBox("Please enter a proper emergency number")
            Exit Sub

        End If


        Try

            dsNewRow.Item("CustName") = name

            dsNewRow.Item("UnitNum") = unit

            dsNewRow.Item("BlkName") = blk

            dsNewRow.Item("EmerNum") = eNo

            ds.Tables("Alarms").Rows.Add(dsNewRow)

            conn.Open()

            da.Update(ds, "Alarms")

            conn.Close()

            MsgBox("Your Personal Information have been updated")

            txtName.Text = ""
            txtBlock.Text = ""
            txtUnit.Text = ""
            txtNum.Text = ""

            btnEdit.Enabled = False


        Catch ex As Exception

        End Try

    End Sub

    Private Sub btnClear_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnClear.Click

        txtName.Clear()
        txtBlock.Clear()
        txtUnit.Clear()
        txtNum.Clear()

    End Sub

    Private Sub btnEdit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnEdit.Click

        txtName.ReadOnly = False
        txtBlock.ReadOnly = False
        txtUnit.ReadOnly = False
        txtNum.ReadOnly = False

        btnEdit.Visible = False
        btnClear.Enabled = True
        btnUpdate.Visible = True
        btnDel.Enabled = False

    End Sub

    Private Sub btnUpdate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnUpdate.Click

        Try
            Dim i As Integer

            For i = 0 To (ds.Tables("Alarms").Rows.Count - 1)

                If DataGridView1.Rows(i).Cells("Selection").Value IsNot System.DBNull.Value Then

                    If DataGridView1.Rows(i).Cells("Selection").Value = True Then


                        conn.Open()

                        Dim nameCommand As SqlCommand = conn.CreateCommand()
                        nameCommand.CommandText = _
                       "UPDATE Alarms SET CustName = '" & txtName.Text & "', BlkName= '" & txtBlock.Text & "', UnitNum = '" & txtUnit.Text & "', EmerNum= '" & txtNum.Text & "' WHERE CustID = '" & TextBox1.Text & "'"

                        nameCommand.ExecuteNonQuery()
                        ds.AcceptChanges()
                        da.Update(ds, "Alarms")
                        conn.Close()

                        MsgBox("Customer Information updated")

                        btnUpdate.Visible = False
                        btnInsert.Enabled = True
                        btnClear.Enabled = True
                        btnEdit.Visible = True
                        btnEdit.Enabled = False

                        txtName.Text = ""
                        txtBlock.Text = ""
                        txtUnit.Text = ""
                        txtNum.Text = ""

                        DataGridView1.Rows(i).Cells("Selection").Value = DBNull.Value


                    End If

                End If


            Next i

        Catch ex As Exception
            MessageBox.Show(ex.Message)
        End Try


    End Sub

    Private Sub btnSelect_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSelect.Click


        Dim i As Integer


        'Change to txtbox format

        Dim ds As DataTable = CType(DataGridView1.DataSource, DataTable)

        txtName.Text = ""
        txtBlock.Text = ""
        txtUnit.Text = ""
        txtNum.Text = ""

        For i = 0 To (ds.Rows.Count - 1)

            If DataGridView1.Rows(i).Cells("Selection").Value IsNot System.DBNull.Value Then

                If DataGridView1.Rows(i).Cells("Selection").Value = True Then

                    txtName.Text += DataGridView1.Rows(i).Cells("CustName").Value.ToString()
                    txtBlock.Text += DataGridView1.Rows(i).Cells("BlkName").Value.ToString()
                    txtUnit.Text += DataGridView1.Rows(i).Cells("UnitNum").Value.ToString()
                    txtNum.Text += DataGridView1.Rows(i).Cells("EmerNum").Value.ToString()
                    TextBox1.Text += DataGridView1.Rows(i).Cells("CustID").Value.ToString()

                    txtName.ReadOnly = True
                    txtBlock.ReadOnly = True
                    txtUnit.ReadOnly = True
                    txtNum.ReadOnly = True

                    btnInsert.Enabled = False
                    btnClear.Enabled = False
                    btnEdit.Enabled = True
                    btnDel.Enabled = True

                End If

            End If

        Next i


    End Sub

  
End Class