IIS 7.5自定义错误页面不适用于具有扩展名的文件

I am facing a starnge issue with one of my server, I've setup the custom error pages however error pages are not showing up when I have file extension in URL for example it does not work for somedomain.com/abcd.aspx or somedomain.com/abcd.aspx, it just show me blank page.I am facing a starnge issue with one of my serv