Not sure if this belongs in SharePoint or IIS, but here's the deal...
I had some problems with the SharePoint 2010 and re-ran the SharePoint Products Config tool... Oops.
In any case, I detached from the farm (I'm running it all on one machine, by the way), finally re-attached and ran the config tool. At first, I had the problem of no access to the Central Admin, but had access to the Web App. Not having learned my mistake the first time, I re-ran the config tool and now have the opposite problem - access to Central Admin without the Web App. When I try to access the web app, I get a 500 error with the following stack trace saying "The farm is unavailable."
01.[InvalidOperationException: The farm is unavailable.]
02. Microsoft.SharePoint.Administration.Claims.SPSecurityTokenServiceManager.get_Local() +24119900
03. Microsoft.SharePoint.IdentityModel.SPTokenCache..ctor() +34
04.
05.[TargetInvocationException: Exception has been thrown by the target of an invocation.]
06. System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandle& ctor, Boolean& bNeedSecurityCheck) +0
07. System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean fillCache) +146
08. System.RuntimeType.CreateInstanceImpl(Boolean publicOnly, Boolean skipVisibilityChecks, Boolean fillCache) +298
09. System.Activator.CreateInstance(Type type, Boolean nonPublic) +79
10. System.RuntimeType.CreateInstanceImpl(BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes) +10364331
11. System.Activator.CreateInstance(Type type, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture) +28
12. Microsoft.IdentityModel.Configuration.CustomTypeElement.Resolve(CustomTypeElement customTypeElement, Object[] arguments) +908
13.
14.[ConfigurationErrorsException: ID0012: Failed to create an instance of 'Microsoft.SharePoint.IdentityModel.SPTokenCache, Microsoft.SharePoint.IdentityModel, Version=14.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c' from configuration.]
15. Microsoft.IdentityModel.Configuration.CustomTypeElement.Resolve(CustomTypeElement customTypeElement, Object[] arguments) +1370069
16. Microsoft.IdentityModel.Configuration.ServiceConfiguration.LoadHandlers(ServiceElement serviceElement) +1160
17. Microsoft.IdentityModel.Configuration.ServiceConfiguration.LoadConfiguration(ServiceElement element) +843
18. Microsoft.IdentityModel.Configuration.ServiceConfiguration..ctor() +317
19. Microsoft.IdentityModel.Web.FederatedAuthentication.get_ServiceConfiguration() +120
20. Microsoft.IdentityModel.Web.HttpModuleBase.Init(HttpApplication context) +17
21. System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers) +480
22. System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context) +336
23. System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context) +350
24. System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext) +382
25.
26.[HttpException (0x80004005): ID0012: Failed to create an instance of 'Microsoft.SharePoint.IdentityModel.SPTokenCache, Microsoft.SharePoint.IdentityModel, Version=14.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c' from configuration.]
27. System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +11297830
28. System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +88
29. System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +4336948