Server Error - Login Failed - Plz Help

I wrote a code to check and validate the username and password against the database and redirect the user based on the user flag as follows:





Dim MyConnection As SqlConnection


Try


If Page.IsValid Then


Dim strUsername As String = txtUsername.Text


Dim strPassword As String = txtPassword.Text


Dim DS As DataSet





Dim MyCommand As SqlDataAdapter





Dim SelectCommand As String = "select userid, flag from employees where username = @login and password = @password"





MyConnection = New SqlConnection("Data Source=localhost;Integrated Security=SSPI;" & _


"Initial Catalog=rfd;")


MyCommand = New SqlDataAdapter(SelectCommand, MyConnection)





MyCommand.SelectCommand.Parameters.Add(New SqlParameter("@login", SqlDbType.Char, 10))


MyCommand.SelectCommand.Parameters("@login").Value = strUsername





MyCommand.SelectCommand.Parameters.Add(New SqlParameter("@password", SqlDbType.Char, 10))


MyCommand.SelectCommand.Parameters("@password").Value = strPassword





DS = New DataSet





MyCommand.Fill(DS)


'MyConnection.Close()





If DS.Tables(0).Rows.Count = 1 Then


Dim flag As String = DS.Tables(0).Rows(0)("flag")


Dim id As Integer = DS.Tables(0).Rows(0)("userid")





Session.Add("flag", flag)


If flag = "u" Then


Session.Add("userid", id)


Session.Add("Page", "user")


Response.Redirect("user_index.aspx")


ElseIf flag = "pl" Then


Session.Add("userid", id)


Session.Add("Page", "pl_index")


Response.Redirect("PL_index.aspx")


End If


Else


msg1.Style("color") = "red"


msg1.Text = "Username or Password incorrect: Please Try again"


End If


End If


Finally


Session.Timeout = 10


MyConnection.Close()


End Try





End Sub





However, when I run it, it points as the line " MyCommand.Fill(DS)" and said Server Error - Login failed for user/aspnet. Where should look and what should I ckeck? Please help me !