Server Error in '/' Application.

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Line 422:        using (SiteCmsDataContext db = new SiteCmsDataContext())
Line 423:        {
Line 424:            var temp = db.ClassInfo.Where(w => w.ClassId == classId).SingleOrDefault();
Line 425:            return temp;
Line 426:        }

[Win32Exception (0x80004005): The network path was not found]

[SqlException (0x80131904): A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)]
   System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, UInt32 waitForMultipleObjectsTimeout, Boolean allowCreate, Boolean onlyOneCheckConnection, DbConnectionOptions userOptions, DbConnectionInternal& connection) +357
   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
   System.Data.Linq.SqlClient.SqlConnectionManager.UseConnection(IConnectionUser user) +43
   System.Data.Linq.SqlClient.SqlProvider.get_IsSqlCe() +42
   System.Data.Linq.SqlClient.SqlProvider.InitializeProviderMode() +22
   System.Data.Linq.SqlClient.SqlProvider.System.Data.Linq.Provider.IProvider.Execute(Expression query) +58
   System.Data.Linq.DataQuery`1.System.Linq.IQueryProvider.Execute(Expression expression) +58
   System.Linq.Queryable.SingleOrDefault(IQueryable`1 source) +220
   SiteClass.getClassInfoDetail(Int32 classId) in c:\webhosting\data\App_Code\SiteClass.cs:424
   Index.Page_Load(Object sender, EventArgs e) in c:\webhosting\data\newdetail.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