The system cannot find the file specified

[Win32Exception (0x80004005): The system cannot find the file specified]

[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) +353
   System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal& connection) +118
   System.Data.ProviderBase.DbConnectionFactory.TryGetConnection(DbConnection owningConnection, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal oldConnection, DbConnectionInternal& connection) +268
   System.Data.ProviderBase.DbConnectionInternal.TryOpenConnectionInternal(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, DbConnectionOptions userOptions) +315
   System.Data.SqlClient.SqlConnection.TryOpenInner(TaskCompletionSource`1 retry) +128
   System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry) +265
   System.Data.SqlClient.SqlConnection.Open() +133
   System.Data.Entity.Infrastructure.Interception.InternalDispatcher`1.Dispatch(TTarget target, Action`2 operation, TInterceptionContext interceptionContext, Action`3 executing, Action`3 executed) +104
   System.Data.Entity.Infrastructure.Interception.DbConnectionDispatcher.Open(DbConnection connection, DbInterceptionContext interceptionContext) +503
   System.Data.Entity.SqlServer.<>c__DisplayClass1.<Execute>b__0() +18
   System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute(Func`1 operation) +234
   System.Data.Entity.Core.EntityClient.EntityConnection.Open() +322

[EntityException: The underlying provider failed on Open.]
   System.Data.Entity.Core.EntityClient.EntityConnection.Open() +743
   System.Data.Entity.Core.Objects.ObjectContext.EnsureConnection(Boolean shouldMonitorTransactions) +167
   System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction(Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess) +63
   System.Data.Entity.Core.Objects.<>c__DisplayClass3.<GetResults>b__1() +203
   System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute(Func`1 operation) +234
   System.Data.Entity.Core.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption) +357
   System.Data.Entity.Core.Objects.ObjectQuery`1.<System.Collections.Generic.IEnumerable<T>.GetEnumerator>b__0() +30
   System.Data.Entity.Internal.LazyEnumerator`1.MoveNext() +39
   System.Collections.Generic.List`1..ctor(IEnumerable`1 collection) +453
   System.Linq.Enumerable.ToList(IEnumerable`1 source) +73
   ViPortal.Core.Providers.SqlServer.SiteProvider.SiteProvider.ChildSites(Site site) in d:\MyProject\Portal\NghiNh\ViPortal\ViPortal\ViPortal.Core.Providers.SqlServer\SiteProvider\SiteProvider.cs:324
   ViPortal.Core.Providers.SqlServer.SiteProvider.SiteProvider.CascadedChildSites(Site site) in d:\MyProject\Portal\NghiNh\ViPortal\ViPortal\ViPortal.Core.Providers.SqlServer\SiteProvider\SiteProvider.cs:309
   ViPortal.Core.Providers.SqlServer.SiteProvider.SiteProvider.AllSites() in d:\MyProject\Portal\NghiNh\ViPortal\ViPortal\ViPortal.Core.Providers.SqlServer\SiteProvider\SiteProvider.cs:305
   ViPortal.Core.Providers.SqlServer.SiteProvider.SiteProvider.GetDomainTable() in d:\MyProject\Portal\NghiNh\ViPortal\ViPortal\ViPortal.Core.Providers.SqlServer\SiteProvider\SiteProvider.cs:243
   ViPortal.Core.Providers.SqlServer.SiteProvider.SiteProvider.GetSiteByHostNameNPath(String hostName, String requestPath) in d:\MyProject\Portal\NghiNh\ViPortal\ViPortal\ViPortal.Core.Providers.SqlServer\SiteProvider\SiteProvider.cs:266
   ViPortal.Core.Web.FrontHttpRequestWrapper.ResolveSite() in d:\Projects\Visualstudio\Projects\ViPortal\ViPortal\ViPortal.Core\Web\FrontHttpRequestWrapper.cs:127
   ViPortal.Core.Web.FrontHttpContextWrapper.get_Request() in d:\Projects\Visualstudio\Projects\ViPortal\ViPortal\ViPortal.Core\Web\FrontHttpContextWrapper.cs:24
   System.Web.Routing.RouteCollection.GetRouteData(HttpContextBase httpContext) +61
   System.Web.Routing.UrlRoutingModule.PostResolveRequestCache(HttpContextBase context) +73
   ViPortal.Core.Web.FrontUrlRoutingModule.application_PostResolveRequestCache(Object sender, EventArgs e) in d:\Projects\Visualstudio\Projects\ViPortal\ViPortal\ViPortal.Core\Web\FrontUrlRoutingModule.cs:19
   System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +142
   System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step) +75
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +93