ASP。位于IIS7上的NET应用程序，它忽略自定义错误并返回到IIS错误

I have a C# web forms ASP.NET 4.0 web application that uses Routing for URLs for some reason custom errors defined in the system.web section of my web.config is entirely ignored and it will fall back the IIS errors.I have a C# web forms ASP.NET 4.0 web applicati