問題描述：
Server Error in '/' Application.
Runtime Error
Description: An application error occurred on the server. The current custom error settings for this application prevent the details of the application error from being viewed remotely (for security reasons). It could, however, be viewed by browsers running on the local server machine.
Details: To enable the details of this specific error message to be viewable on remote machines, please create a <customErrors> tag within a "web.config" configuration file located in the root directory of the current web application. This <customErrors> tag should then have its "mode" attribute set to "Off".
<!-- Web.Config Configuration File -->
<configuration>
<system.web>
<customErrors mode="Off"/>
</system.web>
</configuration>
Notes: The current error page you are seeing can be replaced by a custom error page by modifying the "defaultRedirect" attribute of the application's <customErrors> configuration tag to point to a custom error page URL.
<!-- Web.Config Configuration File -->
<configuration>
<system.web>
<customErrors mode="RemoteOnly" defaultRedirect="mycustompage.htm"/>
</system.web>
</configuration>
新建站點的時候，經常碰到這個問題，搜索之后就是修改配置文件，但是效果不好，有后遺症。
最終解決方案：
.檢查iis—web服務擴展--ASP.NET v2.0.50727和Active Server Pages有沒有設置允許
（如果沒有服務擴展重新注冊IIS服務擴展，在“開始”-“運行”里輸入如入命令，回車C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\aspnet_regiis -i -enable）
2.控制面板--管理工具--服務--asp.netstate service 設置為自動，並啟動
1執行后如果不行最好重新建立一個虛擬目錄或網站瀏覽
最近出現應該是更新了.net的補丁造成的