Technical Tutorials on MS Dynamics Axapta 2012,D365 FnO

Problem I am Getting below Errors on AIF Web service enabling for custom class in Ax 2012. 1. Application pool 'MicrosoftDynamicsAXAif60' is being automatically disabled due to a series of failures in the process(es) serving that application pool. 2. There was an error during processing of the managed application service auto-start for configuration path: 'MACHINE/WEBROOT/APPHOST/Default Web Site/MicrosoftDynamicsAXAif60'. The error message returned is: 'An initialization error occurred while trying to preload an application. Exception: System.Configuration.ConfigurationErrorsException Message: Duplicate type with name 'Dynamics.Ax.Application.NewItem' in assembly 'Dynamics.Ax.Application, Version=6.3.1000.309, Culture=neutral, PublicKeyToken=null'. StackTrace:    at System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective)    at System.Web.Configuration.CompilationSection.LoadAllAssembl...