Error Event with ID=3

This morning I was greeted with the error in Application log of Event Log on my dev environment:
WebHost failed to process a request.
 Sender Information: System.ServiceModel.Activation.HostedHttpRequestAsyncResult/32074454
 Exception: System.ServiceModel.ServiceActivationException: The service '/_vti_bin/ServiceName/ServiceName.svc' cannot be activated due to an exception during compilation.  The exception message is: The type 'ServiceName', provided as the Service attribute value in the ServiceHost directive, or provided in the configuration element system.serviceModel/serviceHostingEnvironment/serviceActivations could not be found.. ---> System.InvalidOperationException: The type 'ServiceName', provided as the Service attribute value in the ServiceHost directive, or provided in the configuration element system.serviceModel/serviceHostingEnvironment/serviceActivations could not be found.
   at System.ServiceModel.Activation.ServiceHostFactory.CreateServiceHost(String constructorString, Uri[] baseAddresses)
   at System.ServiceModel.ServiceHostingEnvironment.HostingManager.CreateService(String normalizedVirtualPath, EventTraceActivity eventTraceActivity)
   at System.ServiceModel.ServiceHostingEnvironment.HostingManager.ActivateService(ServiceActivationInfo serviceActivationInfo, EventTraceActivity eventTraceActivity)
   at System.ServiceModel.ServiceHostingEnvironment.HostingManager.EnsureServiceAvailable(String normalizedVirtualPath, EventTraceActivity eventTraceActivity)
   --- End of inner exception stack trace ---
   at System.Runtime.AsyncResult.End[TAsyncResult](IAsyncResult result)
   at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.End(IAsyncResult result)
 Process Name: w3wp
 Process ID: 17160

I double checked to see whether the type in question really is present in the assembly. I also checked to see whether this assembly has been loaded by w3wp.exe process. Nothing pointed to anything unusual.

Then I went to check IIS log and there I found out that the request returned HTTP status code 401. Turns out that during the night worker process recycled by schedule and I left the SharePoint page opened in my browser. SharePoint page contains a piece of javascript code which periodically calls WCF service deployed in _vti_bin folder. Since browser is not on the same domain as dev environment it prompted for password. There was no one there during the night to enter the password so server returned 401. Once I logged in errors went away. False positive.