暮光女克里斯汀短发:.net（C#）一段写入数据库的程序，帮我改一下

protected void Button4_Click(object sender, EventArgs e)
{
string ConnStr = "Provider = Microsoft.Jet.OLEDB.4.0; Data Source = " + HttpContext.Current.Server.MapPath("datalt.mdb");
string strsql = "select count(*) from userdata where UserID like '" + TextBox1.Text + "'";
OleDbConnection Conn = new OleDbConnection(ConnStr);
OleDbCommand mycommand = new OleDbCommand(strsql, Conn);
Conn.Open();
int flag = (int)mycommand.ExecuteScalar();
Conn.Close();
if (flag == 0)
{
DateTime CreateTime = DateTime.Now;
string strCreateTime = CreateTime.ToString("yyyy-MM-dd hh:mm:ss");
string selectstr = "insert into userdata(UserID,Password,Age,Mail) values ('" + TextBox1.Text + "','" + TextBox2.Text + "','" + TextBox3.Text + "')";
OleDbCommand addcommand = new OleDbCommand(selectstr, Conn);
Conn.Open();
addcommand.ExecuteNonQuery();
Conn.Close();
Response.Redirect("chenggong.aspx");
}
}
调试说是insert into 语法错误，但是相同的insert into 语句在另一段程序里就是可以运行的！我弄了一天也能不出来！
加上'" + TextBox4.Text + "'还是不行，还是说insert into 语句错误。