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: SQL Network Interfaces, error: 25 - 连接字符串无效) 
下面是我．６．ＡＳＰ．ＣＳ的代码，接收５传给来的词，，就如上面的问题！
string id = Session["id"].ToString();
string pw = Session["pw"].ToString();
SqlConnection con = new SqlConnection
("server=.,database=login;uid=sa;pwd=asdin6243;");
con.Open();
SqlCommand cmd = new SqlCommand("select count(*) from login where username='" + id + "'and userpw='" + pw + "'", con);
int count = Convert.ToInt32(cmd.ExecuteScalar());
if (count < 0)
{
Response.Write("<b><font color='red'>非法登陆!</font></b>");
Response.Write("<p><a href='5.aspx'>进入登陆界面></a></p>");
return;
}
else
{
Response.Write("登陆成功");
}
}
}
WEB 。CONFIG配置
<configuration>
<connectionStrings>
<add name="ApplicationServices" connectionString="data source=.\SQLEXPRESS;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|\aspnetdb.mdf;User Instance=true" providerName="System.Data.SqlClient"/>
<add name="ApplicationServices"
connectionString="data source=.\SQLEXPRESS;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|\aspnetdb.mdf;User Instance=true"
providerName="System.Data.SqlClient" />
</connectionStrings>
<system.web>
<compilation debug="false" targetFramework="4.0" />
<authentication mode="Forms">
<for***oginUrl="~/Account/Login.aspx" timeout="2880" />
</authentication>
<membership>
<providers>
<clear/>
<add name="AspNetSqlMembershipProvider" type="System.Web.Security.SqlMembershipProvider" connectionStringName="ApplicationServices"
enablePasswordRetrieval="false" enablePasswordReset="true" requiresQuestionAndAnswer="false" requiresUniqueEmail="false"
maxInvalidPasswordAttempts="5" minRequiredPasswordLength="6" minRequiredNonalphanumericCharacters="0" passwordAttemptWindow="10"
applicationName="/" />
</providers>
</membership>
<profile>
<providers>
<clear/>
<add name="AspNetSqlProfileProvider" type="System.Web.Profile.SqlProfileProvider" connectionStringName="ApplicationServices" applicationName="/"/>
</providers>
</profile>
<roleManager enabled="false">
<providers>
<clear/>
<add name="AspNetSqlRoleProvider" type="System.Web.Security.SqlRoleProvider" connectionStringName="ApplicationServices" applicationName="/" />
<add name="AspNetWindowsTokenRoleProvider" type="System.Web.Security.WindowsTokenRoleProvider" applicationName="/" />
</providers>
</roleManager>
</system.web>
<system.webServer>
<modules runAllManagedModulesForAllRequests="true"/>
</system.webServer>
</configuration>

("server=.,database=login;uid=sa;pwd=asdin6243;"); 分号写成逗号了 server=.;database=login;uid=sa;pwd=asdin6243;