This content is no longer supported in this context - what does this mean?

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I have created a new instance in Umbraco cloud, which I cloned to my local system and then installed the latest uSkinned theme. All works nicely on my local env. However having pushed up changes and deployed new content. My live env is throwing errors:

Request error: The URL returned a 404 (not found):
/umbraco/backoffice/UmbracoApi/Content/GetEmptyByKey

They clear away leaving this (see screengrab below):

Any ideas what I am missing?

Message:
Unhandled controller exception occurred for request ‘“https://nick-lewis-digital.s1.umbraco.io/umbraco/backoffice/api/USNPageName/GetDefault?currentNodeID=-1”’

I looked at the Cloud logs and it shows:

Exception:
System.NullReferenceException: Object reference not set to an instance of an object.
at USNStarterKit.Controllers.USNPageNameController.GetDefault(Int32 currentNodeID)
at lambda_method(Closure , Object , Object )
at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.<>c__DisplayClass6_2.b__2(Object instance, Object methodParameters)
at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.Execute(Object instance, Object arguments)
at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ExecuteAsync(HttpControllerContext controllerContext, IDictionary`2 arguments, CancellationToken cancellationToken)
— End of stack trace from previous location where exception was thrown —


This is a companion discussion topic for the original entry at https://our.umbraco.com/forum/104037-this-content-is-no-longer-supported-in-this-context-what-does-this-mean