ASP.NET Web API Intermittent Service Unavailable

Question

We have an ASP.NET Web API application and an ASP.NET web application that interacts with it.

Both applications are hosted locally with IIS Express. The Web API application interacts with a database via the Entity Framework.

The web application makes a good few requests to the Web API application and the majority of the time, these requests are serviced correctly. However occasionally, and only on certain methods, the web application receives a response of "ServiceUnavailable". Subsequent requests are serviced correctly with "OK" responses.

What could this possibly be?

The .NET code in the Web API method isn't being called on these occasions, so could it be IIS Express sending the response?

Could it be something to do with concurrent requests?

Any help would be greatly appreciated.

Thanks in advance,

Ryan

Errrr... yeh! Security Exception System.Data.Entity.Core.EntityCommandExecutionException: An error occurred while executing the command definition. See the inner exception for details. ---> System.InvalidOperationException: Internal connection fatal error. Error state: 15, Token : 247 — Ryan Penfold
look at the event viewer, check if you are getting any exception, it's hard to diagnose with the current scenario — pedrommuller
Is this because Multiple Active Result Sets needs to be enabled? — Ryan Penfold