未处理的异常: System.InvalidOperationException: 实例失败。

未处理的异常:  System.InvalidOperationException: 实例失败。
   在 System.Data.SqlClient.TdsParser.Connect(ServerInfo serverInfo, SqlInternal
ConnectionTds connHandler, Boolean ignoreSniOpenTimeout, Int64 timerExpire, Bool
ean encrypt, Boolean trustServerCert, Boolean integratedSecurity, SqlConnection
owningObject)
   在 System.Data.SqlClient.SqlInternalConnectionTds.AttemptOneLogin(ServerInfo
serverInfo, String newPassword, Boolean ignoreSniOpenTimeout, Int64 timerExpire,
SqlConnection owningObject)
   在 System.Data.SqlClient.SqlInternalConnectionTds.LoginNoFailover(String host
, String newPassword, Boolean redirectedUserInstance, SqlConnection owningObject
, SqlConnectionString connectionOptions, Int64 timerStart)
   在 System.Data.SqlClient.SqlInternalConnectionTds.OpenLoginEnlist(SqlConnecti
on owningObject, SqlConnectionString connectionOptions, String newPassword, Bool
ean redirectedUserInstance)
   在 System.Data.SqlClient.SqlInternalConnectionTds..ctor(DbConnectionPoolIdent
ity identity, SqlConnectionString connectionOptions, Object providerInfo, String
newPassword, SqlConnection owningObject, Boolean redirectedUserInstance)
   在 System.Data.SqlClient.SqlConnectionFactory.CreateConnection(DbConnectionOp
tions options, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection
owningConnection)
   在 System.Data.ProviderBase.DbConnectionFactory.CreatePooledConnection(DbConn
ection owningConnection, DbConnectionPool pool, DbConnectionOptions options)
   在 System.Data.ProviderBase.DbConnectionPool.CreateObject(DbConnection owning
Object)
   在 System.Data.ProviderBase.DbConnectionPool.UserCreateRequest(DbConnection o
wningObject)
   在 System.Data.ProviderBase.DbConnectionPool.GetConnection(DbConnection ownin
gObject)
   在 System.Data.ProviderBase.DbConnectionFactory.GetConnection(DbConnection ow
ningConnection)
   在 System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection ou
terConnection, DbConnectionFactory connectionFactory)
   在 System.Data.SqlClient.SqlConnection.Open()
   在 DirIndexer.SqlHelper.ExecuteDataTable(String connectionString, CommandType
commandType, String commandText, SqlParameter[] commandParameters) 位置 F:\Code
Database\DirIndexer\SQLHelper.cs:行号 799
   在 DirIndexer.SqlHelper.ExecuteDataTable(String connectionString, CommandType
commandType, String commandText) 位置 F:\CodeDatabase\DirIndexer\SQLHelper.cs:
行号 776
   在 DirIndexer.DAI.RunSqlTable(String sql) 位置 F:\CodeDatabase\DirIndexer\DAI
.cs:行号 80
   在 DirIndexer.Indexer.DoIndexByDB(IndexWriter writer) 位置 F:\CodeDatabase\Di
rIndexer\Indexer.cs:行号 124
   在 DirIndexer.Indexer..ctor(String indexDir) 位置 F:\CodeDatabase\DirIndexer\
Indexer.cs:行号 110
   在 DirIndexer.Indexer.Main(String[] args) 位置 F:\CodeDatabase\DirIndexer\Ind
exer.cs:行号 69

请说明详细的问题所在，和怎么修改！谢谢 --------------------编程问答-------------------- 可能数据库连接字符串有误，请贴出出错代码以及web.config的内容 --------------------编程问答-------------------- public static DataTable ExecuteDataTable(string connectionString, CommandType commandType, string commandText, params SqlParameter[] commandParameters)
{
if( connectionString == null || connectionString.Length == 0 ) throw new ArgumentNullException( "connectionString" );

// Create & open a SqlConnection, and dispose of it after we are done
using (SqlConnection connection = new SqlConnection(connectionString))
{
connection.Open();

// Call the overload that takes a connection in place of the connection string
return ExecuteDataTable(connection, commandType, commandText, commandParameters);
}
}

在 connection.Open(); 出错

<?xml version="1.0" encoding="gb2312"?>
<appConfig>
  <dbconnstr>server=LI-40C72A22C09C\SQLEXPRESS.;uid=sa;pwd=123;database=QSearch</dbconnstr>
</appConfig> --------------------编程问答-------------------- 1.connectionString "server=LI-40C72A22C09C\\SQLEXPRESS.;uid=sa;pwd=123;database=QSearch" string
2.commandType Text System.Data.CommandType
3.commandText "select * from WebContent" string
4.commandParameters null System.Data.SqlClient.SqlParameter[]
5.ConnectionString 由于以前的函数求值超时，函数求值被禁用。必须继续执行才能重新启用函数求值。 string
--------------------编程问答--------------------
刚运行，局部变量是
1.connection {System.Data.SqlClient.SqlConnection} System.Data.SqlClient.SqlConnection
2.ConnectionString"server=LI-40C72A22C09C\\SQLEXPRESS.;uid=sa;pwd=123;database=QSearch" string

3.Database "QSearch" string
4.DataSource "LI-40C72A22C09C\\SQLEXPRESS." string
5.FireInfoMessageEventOnUserErrors false bool
6.ServerVersion “connection.ServerVersion”引发了“System.InvalidOperationException”类型的异常 string {System.InvalidOperationException}
7.base {"无效操作。连接被关闭。"} System.Exception {System.InvalidOperationException}

--------------------编程问答-------------------- 遇到同样的问题，Open函数一执行就卡死，在"SQL Server 組態管理員"那里启用"TCP/IP"和开启1433端口，然后重启SQL SERVER的所有服务就搞定了

补充：.NET技术 ,  ASP.NET