Web.config setup to target 4.5 for correct async behaviorsuggest change
The web.config system.web.httpRuntime must target 4.5 to ensure the thread will renter the request context before resuming your async method.
<httpRuntime targetFramework="4.5" />
Async and await have undefined behavior on ASP.NET prior to 4.5. Async / await will resume on an arbitrary thread that may not have the request context. Applications under load will randomly fail with null reference exceptions accessing the HttpContext after the await. http://stackoverflow.com/questions/24956178/using-httpcontext-current-in-webapi-is-dangerous-because-of-async