[WebAPI] The assembly containing the OwinStartupAttribute cannot be found

The following error occurred when trying to load the app.
- The assembly containing the OwinStartupAttribute cannot be found.
- No Startup or [AssemblyName] could be found. Startup class.
To disable OWIN startup discovery, add the value "false" to appSetting owin:AutomaticAppStartup in web.config.
To specify an OWIN startup assembly, class, or method, add a fully qualified startup class or configuration method name for appSetting owin:AppStartup in web.config.