SelectedIndexChanged To Open A New Form / Not Working

I have a web page with a datagridview where a user should be able to click on the selectindexchanged (in this case a "Select" button) show the results of what they have selected in a label on the second page and also redirect them to that page. Here is the code I have for the vb.net:

Imports System.Data.SqlClient
Imports System.Data
Partial Class _Default
Inherits System.Web.UI.Page
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
TimeDateLabel.Text = String.Format("Today is {0:F}", DateTime.Now)
TextBox1.Focus()
End Sub
Protected Sub whosoncallButton_click(ByVal sender As Object, ByVal e As System.EventArgs) Handles whosoncallButton.Click
Dim dt As New DataTable
Dim da As New SqlDataAdapter
Dim cmd As New SqlCommand
Dim connectionString As String = "Initial Catalog=mdr;Data Source=xxxxx;uid=xxxxx;password=xxxxx"
Dim con As New SqlConnection(connectionString)
con.Open()
cmd.Connection = con
cmd.CommandType = CommandType.StoredProcedure
cmd.CommandText = "getoncall"
cmd.Parameters.AddWithValue("@subschedule", TextBox1.Text)
Try
da.SelectCommand = cmd
da.Fill(dt)
GridView1.DataSource = dt
GridView1.DataBind()
con.Dispose()
Catch ex As Exception
Response.Write("Error:" & ex.Message)
End Try
End Sub
Protected Sub clearButton_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles clearButton.Click
TextBox1.Text = ""
GridView1.DataSource = Nothing
GridView1.DataBind()
End Sub
Protected Sub GridView1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles GridView1.SelectedIndexChanged
Dim row As GridViewRow = GridView1.SelectedRow
Response.Redirect("Default2.aspx?msg=" + row.Cells(1).Text)
End Sub
End Class

I have also added a line to my aspx page for the event handler.

I have debugged this but no matter what I've tried so far, the SelectIndexChanged event isn't firing.