uploading images in formview

Hi, i'm very new to asp.net. I have a problem with my Button1_Click subroutine, it says that the FileUpload1, Label1 and ImageButton1 is not declared when i started to debug. Also, i put these controls in my InsertItem in FormView. Hope you could help me on this.
Btw, the upload will display images as thumbnails
My code in subroutine
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs)
        If Not FileUpload1.HasFile Then
            Label1.Text = "You have not uploaded a file."
        ElseIf CheckExtension(FileUpload1.FileName) = False Then
            Label1.Text = "Only .gifs, and .jpg, please."
        Else
         &nbs ...