我是新手,请教下:以下是C#源代码,不知道什么问题,怎么都连接不上数据库..问是在执行了catch里(已标色)了:
 text = login_username.Text;
            key = login_password.Text;
            string str = "user id=sa;password=xjjy287094;";
           //string str="Trusted_Connection=SSPI;";//自动登陆时使用的

           str += @"initial catalog=St_china_elc;Server=(local)\SQL2005;integrated security=True;";
            //str+=@"Server=WWW-9EB2192731B\SQL2005;initial catalog=St_china_elc;Integrated Security=True;";
            str+="Connect Timeout=30";
            // string str=@"Data Source=WWW-9EB2192731B\SQL2005;Initial Catalog=St_china_elc;Integrated Security=True using System;";
            SqlConnection con = new SqlConnection(str);
            try
            {

                con.Open();
                if (con == null)
                {
                    Response.Redirect("PasswordChange.aspx");
                }
                login_username.Text = "hdu";
                login_password.Text = "dj";
               
                string strsql = "select Users_UserName from Users  where Users_UserName=" + login_username.Text + "and Users_Password=" + login_password.Text;
                SqlDataAdapter da = new SqlDataAdapter(strsql, con);
                DataSet ds = new DataSet();
                int count = da.Fill(ds, "table");
                if (count > 0)
                {
                    lab_test1.Visible = true;
                    Response.Redirect("PasswordChange.aspx");

                }
                else
                {
                    Response.Write("<script>alert('<font color=red>不存在的用户名</font>')");
                    lab_test1.Text = "登陆失败";
                    lab_test1.Visible = true;  

                }
            }
            catch (Exception ex)
            {
                lab_test1.Text = "连接\\登陆失败";
                lab_test1.Visible = true;
               
            }
            finally
            {
                login_username.Text = "hdu";
                login_password.Text = "dj";
                con.Close();
            }
        }

int count = da.Fill(ds, "table");
这里应该写错了吧，你查询的是Users 表，而你写的是table数据库没有那个表报错

你跟一下，看错在什么地方啊
最可能出错的地方是连接字符串

首先，确认你的数据库连接字符串没问题。
其次，这句话有问题
string strsql = "select Users_UserName from Users  where Users_UserName='" + login_username.Text + "' and Users_Password='" + login_password.Text + "'";
再次，用SqlDataAdapter时，无需对SqlConnection进行打开关闭工作。
最后，下面的判断有问题

int count = da.Fill(ds, "table");
                if (count > 0)
                {
                    lab_test1.Visible = true;
                    Response.Redirect("PasswordChange.aspx");

                }

==================>

da.Fill(ds, "table");
                if (ds.Tables[0].Rows.Count> 0)
                {
                    lab_test1.Visible = true;
                    Response.Redirect("PasswordChange.aspx");

                }

完全同意楼上意见！！！