登陆页面不跳转到mainForm,自动停止调试程序，哪里错了？？？

Question

if (this.txtUserName.Text == "")
                {
                    MessageBox.Show("用户名不能为空！");                }
                else
                {
                    if (this.txtUserPwd.Text == "")
                    {
                        MessageBox.Show("密码不能为空！");
                    }
                    else
                    {
                        try
                       {
                            string str = "select UserPwd from tb_User where UserName ='" + this.txtUserName.Text.ToString() + "'";
                            SqlConnection con = DB.createConnection();
                            SqlDataAdapter thisDataAdapter = new SqlDataAdapter(str, con);
                            DataSet myDataset = new DataSet();
                            thisDataAdapter.Fill(myDataset, "userLogin");                            string dataString=myDataset.Tables["userLogin"].Rows[0][0].ToString();
                            string frmString=this.txtUserPwd.Text.Trim();                            if (dataString == frmString)
                            {
                                frmMain main = new frmMain();
                                this.Close();
                                main.Show();
                            }
                            else
                            {
                                MessageBox.Show("用户名或密码输入不正确！！！");
                            }
                            
                        }
                        catch (Exception eLogin)
                        {
                            MessageBox.Show("用户不存在，请重新输入！");
                            txtUserName.Text = txtUserPwd.Text = "";
                            txtUserName.Focus();
                            
                        }
登陆页面不跳转到mainForm,自动停止调试程序，哪里错了？？？

Answer 1

SqlConnection con = DB.createConnection(); 是DB类中的createConnection()方法，这里没错哪里出错了呢 

Answer 2

                               frmMain main = new frmMain(); 
                                this.Hiden();
                                main.Show();