Разбивая мою голову этим, вчера это работало нормально, а сегодня, похоже, сломалось:

Эта строка генерирует ошибку:

@if (Roles.IsUserInRole(HttpContext.Current.User.Identity.Name, "Admin"))

ошибка: невозможно подключиться к базе данных SQL Server.

Целое исключение:

System.Web.HttpException was unhandled by user code
  HResult=-2147467259
  Message=Unable to connect to SQL Server database.
  Source=System.Web
  ErrorCode=-2147467259
  WebEventCode=0
  StackTrace:
       at System.Web.DataAccess.SqlConnectionHelper.CreateMdfFile(String fullFileName, String dataDir, String connectionString)
       at System.Web.DataAccess.SqlConnectionHelper.EnsureDBFile(String connectionString)
       at System.Web.DataAccess.SqlConnectionHelper.GetConnection(String connectionString, Boolean revertImpersonation)
       at System.Web.Security.SqlRoleProvider.GetRolesForUser(String username)
       at WebMatrix.WebData.SimpleRoleProvider.GetRolesForUser(String username)
       at System.Web.Security.RolePrincipal.IsInRole(String role)
       at System.Web.Security.Roles.IsUserInRole(String username, String roleName)
       at ASP._Page_Views_Shared__LoginPartial_cshtml.Execute() in e:\LeasingWeb\LeasingWeb\Views\Shared\_LoginPartial.cshtml:line 10
       at System.Web.WebPages.WebPageBase.ExecutePageHierarchy()
       at System.Web.Mvc.WebViewPage.ExecutePageHierarchy()
       at System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage)
       at System.Web.Mvc.RazorView.RenderView(ViewContext viewContext, TextWriter writer, Object instance)
       at System.Web.Mvc.BuildManagerCompiledView.Render(ViewContext viewContext, TextWriter writer)
       at System.Web.Mvc.HtmlHelper.RenderPartialInternal(String partialViewName, ViewDataDictionary viewData, Object model, TextWriter writer, ViewEngineCollection viewEngineCollection)
       at System.Web.Mvc.Html.PartialExtensions.Partial(HtmlHelper htmlHelper, String partialViewName, Object model, ViewDataDictionary viewData)
       at System.Web.Mvc.Html.PartialExtensions.Partial(HtmlHelper htmlHelper, String partialViewName)
       at ASP._Page_Views_Shared__Layout_cshtml.Execute() in e:\LeasingWeb\LeasingWeb\Views\Shared\_Layout.cshtml:line 35
       at System.Web.WebPages.WebPageBase.ExecutePageHierarchy()
       at System.Web.Mvc.WebViewPage.ExecutePageHierarchy()
       at System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage)
       at System.Web.WebPages.WebPageBase.c__DisplayClass7.b__6(TextWriter writer)
       at System.Web.WebPages.HelperResult.WriteTo(TextWriter writer)
       at System.Web.WebPages.WebPageBase.Write(HelperResult result)
       at System.Web.WebPages.WebPageBase.RenderSurrounding(String partialViewName, Action`1 body)
       at System.Web.WebPages.WebPageBase.PopContext()
       at System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage)
       at System.Web.Mvc.RazorView.RenderView(ViewContext viewContext, TextWriter writer, Object instance)
       at System.Web.Mvc.BuildManagerCompiledView.Render(ViewContext viewContext, TextWriter writer)
       at System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context)
       at System.Web.Mvc.ControllerActionInvoker.InvokeActionResult(ControllerContext controllerContext, ActionResult actionResult)
       at System.Web.Mvc.ControllerActionInvoker.c__DisplayClass1a.b__17()
       at System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilter(IResultFilter filter, ResultExecutingContext preContext, Func`1 continuation)
  InnerException: System.Web.HttpException
       HResult=-2147467259
       Message=Unable to connect to SQL Server database.
       Source=System.Web
       ErrorCode=-2147467259
       WebEventCode=0
       StackTrace:
            at System.Web.Management.SqlServices.GetSqlConnection(String server, String user, String password, Boolean trusted, String connectionString)
            at System.Web.Management.SqlServices.SetupApplicationServices(String server, String user, String password, Boolean trusted, String connectionString, String database, String dbFileName, SqlFeatures features, Boolean install)
            at System.Web.Management.SqlServices.Install(String database, String dbFileName, String connectionString)
            at System.Web.DataAccess.SqlConnectionHelper.CreateMdfFile(String fullFileName, String dataDir, String connectionString)
       InnerException: System.Data.SqlClient.SqlException
            HResult=-2146232060
            Message=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: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)
            Source=.Net SqlClient Data Provider
            ErrorCode=-2146232060
            Class=20
            LineNumber=0
            Number=-1
            Server=""
            State=0
            StackTrace:
                 at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
                 at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose)
                 at System.Data.SqlClient.TdsParser.Connect(ServerInfo serverInfo, SqlInternalConnectionTds connHandler, Boolean ignoreSniOpenTimeout, Int64 timerExpire, Boolean encrypt, Boolean trustServerCert, Boolean integratedSecurity, Boolean withFailover)
                 at System.Data.SqlClient.SqlInternalConnectionTds.AttemptOneLogin(ServerInfo serverInfo, String newPassword, SecureString newSecurePassword, Boolean ignoreSniOpenTimeout, TimeoutTimer timeout, Boolean withFailover)
                 at System.Data.SqlClient.SqlInternalConnectionTds.LoginNoFailover(ServerInfo serverInfo, String newPassword, SecureString newSecurePassword, Boolean redirectedUserInstance, SqlConnectionString connectionOptions, SqlCredential credential, TimeoutTimer timeout)
                 at System.Data.SqlClient.SqlInternalConnectionTds.OpenLoginEnlist(TimeoutTimer timeout, SqlConnectionString connectionOptions, SqlCredential credential, String newPassword, SecureString newSecurePassword, Boolean redirectedUserInstance)
                 at System.Data.SqlClient.SqlInternalConnectionTds..ctor(DbConnectionPoolIdentity identity, SqlConnectionString connectionOptions, SqlCredential credential, Object providerInfo, String newPassword, SecureString newSecurePassword, Boolean redirectedUserInstance, SqlConnectionString userConnectionOptions)
                 at System.Data.SqlClient.SqlConnectionFactory.CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection, DbConnectionOptions userOptions)
                 at System.Data.ProviderBase.DbConnectionFactory.CreateNonPooledConnection(DbConnection owningConnection, DbConnectionPoolGroup poolGroup, DbConnectionOptions userOptions)
                 at System.Data.ProviderBase.DbConnectionFactory.TryGetConnection(DbConnection owningConnection, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal& connection)
                 at System.Data.ProviderBase.DbConnectionClosed.TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, DbConnectionOptions userOptions)
                 at System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry)
                 at System.Data.SqlClient.SqlConnection.Open()
                 at System.Web.Management.SqlServices.GetSqlConnection(String server, String user, String password, Boolean trusted, String connectionString)
            InnerException: 

И, как я уже сказал, это работало в течение нескольких дней, я использовал пользовательскую БД по умолчанию, которая создается при создании нового проекта MVC4.

Web.config:

Ошибка клиента:

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: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)

Таблицы БД выглядят хорошо, пользователи и роли существуют и остаются такими же, как и раньше.