System.Data.EntityException: The underlying provider failed on Open.

场景：IIS默认站点建立程序，使用Windows集成身份验证方式，连接SQLServer数据库也是采用集成身份验证。我报“System.Data.EntityException: The underlying provider failed on Open.”这个错误是因为计算机登录密码改过，导致之前应用程序池设置的凭证错误，解决办法：把应用程序池的登录凭证也修改一下改成和计算机登录密码一样，这样程序就好了。

步骤：

　　新增一个应用程序：

　　IIS Default Web Site-->Add Application-->Application Pool-->ASP.NET V4.0 Integrated

　　修改应用程序池的凭证：

　　Application Pool-->ASP.NET V4.0 Integrated-->Advanced Settings-->Process Model-->Identity-->Customer account-->Set Credentials-->Set UserName=Cumputer LoginName,Password=Cumputer Login Password-->Click OK

　　配置文件

<appSettings>
　　　　<add key="CreditCheckGatewayDB" value="Server=fscnbesd0001;Database=CreditCheckGateway;Integrated Security=SSPI;" />
  　　</appSettings>

　　C#读取连接字符串

        static public string GetCupCreditCheckConnectionString
        {
            get
            {
                return string.Format("metadata=res://*/CupModel.csdl|res://*/CupModel.ssdl|res://*/CupModel.msl;provider=System.Data.SqlClient;provider connection string="{0}";", ConfigurationManager.AppSettings["CreditCheckGatewayDB"]);
            }
        }

　　或者配置文件直接写

<appSettings>
    <add key="CupCreditCheckDB" value="metadata=res://*/CupModel.csdl|res://*/CupModel.ssdl|res://*/CupModel.msl;provider=System.Data.SqlClient;provider connection string=&quot;Server=fscnbesd0001;Database=CreditCheckGateway;Integrated Security=SSPI&quot;" providerName="System.Data.EntityClient" />
</appSettings>

 <connectionStrings>
    <add name="CupCreditCheckDB" connectionString="metadata=res://*/CupModel.csdl|res://*/CupModel.ssdl|res://*/CupModel.msl;provider=System.Data.SqlClient;provider connection string=&quot;Server=fscnbesd0001;Database=CreditCheckGateway;Integrated Security=SSPI&quot;" providerName="System.Data.EntityClient" />
</connectionStrings>