未处理oledbexception，怎么改？

private void button1_Click(object sender, EventArgs e)
{
if (name.Text.Trim() == "" || password.Text.Trim() == "")
MessageBox.Show("请输入用户名和密码", "提示");
else
{
oleConnection1.Open();
OleDbCommand cmd = new OleDbCommand("", oleConnection1);
string sql = "select * from user where uname='" + name.Text.Trim() + "' and ucode='" + password.Text.Trim() + "'";
cmd.CommandText = sql;
if (null != cmd.ExecuteScalar())
{
//隐藏登录窗口
this.Visible = false;
//创建并打开主界面
main main = new main();
main.Tag = this.FindForm();
OleDbDataReader dr;
cmd.CommandText = sql;
dr = cmd.ExecuteReader();
dr.Read();
main.ShowDialog();
}
else
MessageBox.Show("用户名或密码错误", "警告");
}
oleConnection1.Close();
}
}
}