腦容量太小

參考Apache log4net FAQ

A windows service runs as a user account specified in the services control panel. This account may have restricted permissions, make sure that the account has permission to create and write to files in the directory chosen for logging.

A windows service is launched by windows. The current directory in a service is set to the windows system directory (e.g. C:\Windows\System32). If you are loading the configuration file from the current directory then be aware that this path will not be the location of your assemblies. The best way to get the path to your assemblies is to use AppDomain.BaseDirectory. Note that the log4net internals never use the current directory.

通常我會將log4net的設定檔與assembly放在同一個目錄，在一般的應用程式可以使用

XmlConfigurator.Configure(new System.IO.FileInfo("log4netConfig.xml"));

來載入設定檔

但由於Windows service是由windows啟動，所以預設目錄會設為系統目錄(通常是C:\Windows\System32)，如此一來，使用上面的敘述將無法正確載入設定檔，取得assembly路徑的最佳方式是使用AppDomain.CurrentDomain.BaseDirectory，因此建議使用以下的方式載入設定檔

XmlConfigurator.Configure(new System.IO.FileInfo(AppDomain.CurrentDomain.BaseDirectory + "\\log4netConfig.xml"));