如何捕获触发自定义错误页面的ASP.NET错误，但不捕获Application_Error

I have an ASP.NET application using custom errors. There is one error that occurs that I can't seem to get any information about. When the error happens, it does trigger the custom error page, but for some reason it doesn't trigger Page_Error or Application_Error. If I turn CustomErrors Off completely, I get absolutely no feedback at all. The only feedback I ever have gotten up until now is the redirect to the Custom Error Page.I have an ASP.NET application using custom erro