Why Am I Getting "Must Declare The Scalar Variable Errors At Run Time"

Public Class Form1

    'Dim sqlconnection As SqlConnection
    Dim oledbconnection As OleDbConnection
    Dim dsusers As DataSet
    Dim oleda As OleDbDataAdapter
    Const oleconstring As String = "Initial Catalog=db1;Data Source=vmsvr01;Integrated Security=SSPI;provider=sqloledb"
    Const sqlselect As String = "select * from users"
    Const sqldelete As String = "delete from users where [userid] = @userid"
    Const sqlinsert As String = "insert into users ([firstname],[lastname],[username],[password]) values (@firstname,@lastname,@username,@password)"
    Const sqlupdate As String = "update users set [firstname] = @firstname, [lastname] = @lastname, [username] = @username, [password] = @password where [userid] = @userid"
    Dim userid, si As Integer
    Dim dr() As DataRow

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        initializeOLEDB()
    End Sub
    Private Sub initializeOLEDB()
        dsusers = New DataSet
        oledbconnection = New OleDbConnection(oleconstring)
        Dim cmddelete = New OleDbCommand(sqldelete, oledbconnection)
        Dim cmdinsert = New OleDbCommand(sqlinsert, oledbconnection)
        Dim cmdupdate = New OleDbCommand(sqlupdate, oledbconnection)
        oleda = New OleDbDataAdapter(sqlselect, oledbconnection)
        oleda.DeleteCommand = cmddelete
        oleda.InsertCommand = cmdinsert
        oleda.UpdateCommand = cmdupdate

        cmddelete.Parameters.Add("@userid", OleDbType.Integer, Nothing, "userid")

        cmdinsert.Parameters.Add("@firstname", OleDbType.VarChar, 50, "firstname")
        cmdinsert.Parameters.Add("@lastname", OleDbType.VarChar, 50, "lastname")
        cmdinsert.Parameters.Add("@username", OleDbType.VarChar, 50, "username")
        cmdinsert.Parameters.Add("@password", OleDbType.VarChar, 255, "Password")

        cmdupdate.Parameters.Add("@firstname", OleDbType.VarChar, 50, "firstname")
        cmdupdate.Parameters.Add("@lastname", OleDbType.VarChar, 50, "lastname")
        cmdupdate.Parameters.Add("@username", OleDbType.VarChar, 50, "username")
        cmdupdate.Parameters.Add("@password", OleDbType.VarChar, 255, "Password")
        cmdupdate.Parameters.Add("@userid", OleDbType.Integer, Nothing, "UserID")

        oleda.Fill(dsusers, "users")
        dsusers.Tables!users.Columns!userid.AutoIncrement = True
        dsusers.Tables!users.Columns!userid.AutoIncrementSeed = -1
        dsusers.Tables!users.Columns!userid.AutoIncrementStep = -1
        lb.ValueMember = "userid"
        lb.DisplayMember = "Username"
        lb.DataSource = dsusers.Tables!users
    End Sub
    Private Sub lb_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles lb.SelectedIndexChanged
        If lb.SelectedIndex > -1 Then
            si = lb.SelectedIndex
            userid = CType(lb.SelectedValue.ToString, Integer)
            dr = dsusers.Tables!users.Select("userid = " & userid)
            txtuserid.Text = CType(dr(0)!userid, String)
            txtfirstname.Text = CType(dr(0)!Firstname, String)
            txtlastname.Text = CType(dr(0)!lastname, String)
            txtusername.Text = CType(dr(0)!username, String)
            txtpassword.Text = CType(dr(0)!password, String)
        End If
    End Sub
    Private Sub LinkLabel2_LinkClicked(ByVal sender As System.Object, ByVal e As System.Windows.Forms.LinkLabelLinkClickedEventArgs) Handles LinkLabel2.LinkClicked
        dr(0).Delete()
    End Sub
    Private Sub OK_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles OK.Click
        If dsusers.HasChanges Then
            oleda.Update(dsusers, "Users")
        End If
    End Sub
    Private Sub lladd_LinkClicked(ByVal sender As System.Object, ByVal e As System.Windows.Forms.LinkLabelLinkClickedEventArgs) Handles lladd.LinkClicked
        Dim newdr As DataRow = dsusers.Tables!users.NewRow
        newdr!firstname = txtfirstname.Text
        newdr!lastname = txtlastname.Text
        newdr!username = txtusername.Text
        newdr!password = txtpassword.Text
        dsusers.Tables!users.Rows.Add(newdr)
    End Sub
    Private Sub llsave_LinkClicked(ByVal sender As System.Object, ByVal e As System.Windows.Forms.LinkLabelLinkClickedEventArgs) Handles llsave.LinkClicked
        lb.SelectedIndex = -1
        dr(0)!firstname = txtfirstname.Text
        dr(0)!lastname = txtlastname.Text
        dr(0)!username = txtusername.Text
        dr(0)!password = txtpassword.Text
        lb.SelectedIndex = si
    End Sub
end class