Thinking more...

由於很勇敢地衝了Ubuntu Hardy 的緣故，常常會有很多驚喜～
這幾天是遇到 gnome-settings-daemon 無法啟動的問題，開啟終端機試著以手動方式啟動會出現如下訊息：

The program 'gnome-settings-daemon' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadRequest (invalid request code or no such operation)'.
  (Details: serial 107 error_code 1 request_code 151 minor_code 6)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the --sync command line
   option to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)

爬文以後，發現已經有人回報，從 2.21.9 以後就是如此，但是都還沒有解。
依照訊息的建議，改以如下指令再試試：

gnome-settings-daemon --debug --no-daemon --sync

這樣會丟出比較多的錯誤訊息，這邊只列出關鍵部份：

** (gnome-settings-daemon:20265): DEBUG: Registering GsdXrandrPlugin
** (gnome-settings-daemon:20265): DEBUG: Creating object of type GsdXrandrPlugin
** (gnome-settings-daemon:20265): DEBUG: GsdXrandrPlugin initializing
** (gnome-settings-daemon:20265): DEBUG: Activating xrandr plugin
** (gnome-settings-daemon:20265): DEBUG: Starting xrandr manager
The program 'gnome-settings-daemon' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadRequest (invalid request code or no such operation)'.
  (Details: serial 107 error_code 1 request_code 151 minor_code 6)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the --sync command line
   option to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)

喔～這樣看來應該是是 xrandr 的關係～
xrandr 是用來動態切換螢幕用的，舉例來說，接投影機或是額外螢幕時，就會用到～
不過，我現在用不到，那麼，要怎麼停用這個 plugin 呢?
這就得用 gconf-editor 了，使用 gconf-editor 去把 /apps/gnome_settings_daemon/plugins/xrandr/active 機碼改為 0，然後重新啟動 XServer 即可。