Server Error in '/' Application.

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Line 51:             ConfigurationManager.AppSettings["SQLConnectionString"]))
Line 52:         {
Line 53:             conn.Open();
Line 54: 
Line 55:             using (SqlDataAdapter da = new SqlDataAdapter(sql, conn))

[Win32Exception (0x80004005): The pipe has been ended]

[SqlException (0x80131904): A connection was successfully established with the server, but then an error occurred during the pre-login handshake. (provider: Shared Memory Provider, error: 0 - The pipe has been ended.)]
   System.Data.ProviderBase.DbConnectionPool.UserCreateRequest(DbConnection owningObject, DbConnectionOptions userOptions, DbConnectionInternal oldConnection) +6050879
   System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, UInt32 waitForMultipleObjectsTimeout, Boolean allowCreate, Boolean onlyOneCheckConnection, DbConnectionOptions userOptions, DbConnectionInternal& connection) +1270
   System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal& connection) +79
   System.Data.ProviderBase.DbConnectionFactory.TryGetConnection(DbConnection owningConnection, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal oldConnection, DbConnectionInternal& connection) +201
   System.Data.ProviderBase.DbConnectionInternal.TryOpenConnectionInternal(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, DbConnectionOptions userOptions) +156
   System.Data.ProviderBase.DbConnectionClosed.TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, DbConnectionOptions userOptions) +22
   System.Data.SqlClient.SqlConnection.TryOpenInner(TaskCompletionSource`1 retry) +92
   System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry) +219
   System.Data.SqlClient.SqlConnection.Open() +101
   s1214.GreatDs(String sql) in d:\web\HJH\hk2s.hjhdy.com\s1214.aspx.cs:53
   s1214.Page_Load(Object sender, EventArgs e) in d:\web\HJH\hk2s.hjhdy.com\s1214.aspx.cs:17
   System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +52
   System.Web.UI.Control.OnLoad(EventArgs e) +97
   System.Web.UI.Control.LoadRecursive() +61
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +693