登陆问题，web网站登陆时，在于数据库进行交互时发生错误

清朝的恒星 2019-04-01 12:55:28

具体异常如下：
System.Data.SqlClient.SqlException
HResult=0x80131904
Message=在与 SQL Server 建立连接时出现与网络相关的或特定于实例的错误。未找到或无法访问服务器。请验证实例名称是否正确并且 SQL Server 已配置为允许远程连接。 (provider: Named Pipes Provider, error: 40 - 无法打开到 SQL Server 的连接)
Source=.Net SqlClient Data Provider
StackTrace:
<无法计算异常堆栈跟踪>

内部异常 1:
Win32Exception: 找不到网络路径。

我的项目是用数据库连接类sqlhelper来进行数据库连接的相关操作，
登陆代码如下：
using System;
using System.Collections.Generic;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;

public partial class Login : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{

}
protected void Button1_Click(object sender, EventArgs e)
{

if (this.password.Value.ToString().Trim() == "" || username.Value.ToString().Trim() == "")
{
Response.Write("<script>javascript:alert('请输入完整的信息');history.back();</script>");
Response.End();
}

string UserName = username.Value;
string PWD = this.password.Value;
if (this.DropDownList1.SelectedIndex == 0)
{
string SQL = "select * from Admin where UserName='" + UserName + "' and Password='" + PWD + "'";

SqlDataReader sdr = SqlHelper.ExecuteReader(SqlHelper.SqlConnection, CommandType.Text, SQL);
if (sdr.Read())
{

Session["cx"] = "管理员";
Session["PWD"] = PWD;
Session["UserName"] = sdr["username"].ToString();

Response.Redirect("Index.aspx");

}
else
{
Response.Write("<script>alert('用户名或者密码错误！');document.location=document.location;</script>");

}
}

if (this.DropDownList1.SelectedIndex == 1)
{

string SQL = "select * from Coach where Number='" + UserName + "' and Password='" + PWD + "'";
SqlDataReader sdr = SqlHelper.ExecuteReader(SqlHelper.SqlConnection, CommandType.Text, SQL);
if (sdr.Read())
{

if (sdr["issh"].ToString().Trim() == "是")
{
Session["cx"] = "教练";//权限换为教师
Session["PWD"] = PWD;
Session["UserName"] = UserName;
Response.Redirect("CIndex.aspx");
}
else
{
Response.Write("<script>alert('信息未通过审核请等待管理员审核.');location='javascript:history.go(-1);'</script>");
return;

}

}

else
{
Response.Write("<script>alert('用户名或者密码错误！');document.location=document.location;</script>");
}
}

if (this.DropDownList1.SelectedIndex == 2)
{
string SQL = "select * from Player where Number='" + UserName + "' and Password='" + PWD + "'";
SqlDataReader sdr = SqlHelper.ExecuteReader(SqlHelper.SqlConnection, CommandType.Text, SQL);
if (sdr.Read())
{
Response.Write(sdr["issh"].ToString());
if (sdr["issh"].ToString().Trim() == "是")
{

Session["cx"] = "球员";
Session["PWD"] = PWD;
Session["UserName"] = UserName;
Session["Name"] = sdr["Name"].ToString();
Response.Redirect("PIndex.aspx");
}
else
{
Response.Write("<script>alert('信息未通过审核请等待管理员审核.');location='javascript:history.go(-1);'</script>");
return;

}
}
else
{
Response.Write("<script>alert('用户名或者密码错误！');document.location=document.location;</script>");
}
}

}
protected void Button2_Click(object sender, EventArgs e)
{
Response.Redirect("Reg.aspx");
}
protected void Button3_Click(object sender, EventArgs e)
{
Response.Redirect("Regteacher.aspx");
}
}

数据库是允许远程连接的