I have a site running, that occasional stops working, this only way to get it working again is restarting the site.

The home page contains three sections, each gets its 'page' of data from $http.get to my UmbracoApiController derived Controllers.

Most of the time everything works fine even under load...But for some reason all calls to my controllers fail/YBOD with:

2014-12-04 11:17:15,723 [7] ERROR Umbraco.Core.UmbracoApplicationBase - [Thread 5] An unhandled exception occurred(Source:System.Web.Http.WebHost    
System.NullReferenceException: Object reference not set to an instance of an object.
       at System.Web.Http.WebHost.HttpControllerHandler.EndProcessRequest(IAsyncResult result)
       at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
       at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

Now the code in my controller's method executes, I've added various log outputs before the methods return. Everything in my code seems fine( well it works!).

I'm stuck as how to fix this...I thought it might be UmbracoAPIController's initialisers but my code executes, which points the blame to S.W.H.WebHost...

I've studied UmbracoTraceLog.txt and iislogs and things seem fine, apart from the exception.

Other parts of the site are working master page, partial views, headings etc - it's just the items that get their data via my controllers.

Umbraco version 7.1.6

Has anybody else had any experience with this happening to them?

Anyway to determine what is null?