I cant see the error message

I have this code.when i enter an incorrect name and pass i can't see the error message in label.
 
string cu_usr, cu_pass;
cu_usr = txtuser2.Text.Trim();
cu_pass = txtpass2.Text.Trim();
con.Open();
cmd.Connection = con;
cmd.CommandType = CommandType.StoredProcedure;
cmd.CommandText = "sp_login";
cmd.Parameters.AddWithValue("@cu_username", cu_usr);
cmd.Parameters.AddWithValue("@cu_password", cu_pass);
dr=cmd.ExecuteReader();
if (dr.Read())
{
Session.Add("user", cu_usr);

MasterPage mymaster = (MasterPage)this.Master;
Panel mas ...