webapi调用只有在使用unity DI回收应用程序池时才会失败

我正在调用一个web api服务，该服务仅在我第一次回收应用程序池时失败。之后所有的调用都可以正常工作。

过程是这样的…

Call Service -> return OK

Call Service -> return OK

Call Service -> return OK

进入iis并回收应用程序池(我等待10秒)

Call Service ->发生内部服务器错误。请稍后再试。

Call Service -> return OK

Call Service -> return OK

Call Service -> return OK

…进入iis并回收应用程序池(我等了10秒)呼叫服务-->发生内部服务器错误。请稍后再试。

Call Service -> return OK

Call Service -> return OK

Call Service -> return OK

…

客户端是一个控制台应用程序框架4.0使用这个方法:

        public static object Send(string webAddr, object param)
        {
            HttpUtil.IgnoreBadCertificates();
            HttpWebRequest request = null;
            object result = null;
            request = (HttpWebRequest)WebRequest.Create(webAddr);
            request.ContentType = "application/json; charset=utf-8";
            request.Method = "POST";
            request.Accept = "application/json";
            String u = GetString(a1);
            String p = GetString(a1) + GetString(a2);
            String encoded = System.Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes(u + ":" + p));
            request.Headers.Add("Authorization", "Basic " + encoded);
            using (var streamWriter = new StreamWriter(request.GetRequestStream()))
            {
                var myJsonString = Newtonsoft.Json.JsonConvert.SerializeObject(param);
                streamWriter.Write(myJsonString);
                streamWriter.Flush();
            }
            var response = (HttpWebResponse)request.GetResponse();
            using (var streamReader = new StreamReader(response.GetResponseStream()))
            {
                result = streamReader.ReadToEnd();
            }
            return result;
        }

webapi是framework 4.5:

 public class CambiosController : BaseApiController
    {
        private ICambioService cambioService;
        public CambiosController(ICambioService cambioService)
        {
            this.cambioService = cambioService;
        }
        [HttpPost]
        [Authorize]
        public HttpResponseMessage Post([FromBody] CambioRequest cambioRequest)
        {
            HttpResponseMessage response = null;
            if (cambioRequest == null)
            {
                Exception ex = new ArgumentException("cambioRequest");
                return Request.CreateErrorResponse(HttpStatusCode.BadRequest, ex);
            }
            try
            {
                var result = this.cambioService.EnviarConfiguracion(cambioRequest);
                response = Request.CreateResponse(HttpStatusCode.OK, result);
            }
            catch (Exception ex)
            {
                response = Request.CreateErrorResponse(HttpStatusCode.InternalServerError, ex);
            }
            return response;
        }
        protected override void Dispose(bool disposing)
        {
            if (disposing)
            {
                this.cambioService.Dispose();
            }
            base.Dispose(disposing);
        }

统一配置:

public static void RegisterComponents()
{
    LoggerFacility.Debug(string.Empty, string.Empty, "UnityConfig.RegisterComponents()");
    var container = new UnityContainer();
    container.RegisterTypes(
        AllClasses.FromAssemblies(BuildManager.GetReferencedAssemblies().Cast<Assembly>())
        .Where(x => x.Name != "IUnitOfWork" && x.Name != "IDbContext"),
        WithMappings.FromMatchingInterface, WithName.Default, overwriteExistingMappings: true);
    container.RegisterType<IUnitOfWork, UnitOfWork>(new PerResolveLifetimeManager());
    container.RegisterType<IDbContext, ControlConfigContext>(new PerResolveLifetimeManager());
    GlobalConfiguration.Configuration.DependencyResolver = new UnityDependencyResolver(container);
}

WebApi应用池是framework 4集成模式，作为Network Service运行。ProcessModel Idle Timeout (minutes 0)唯一的配置从默认更改。IIS 7.5