Sometimes, when you want to shut down or restart Windows XP, you may see a dialog similar to the one shown in the picture. Even worse, this may happen persistently, thus preventing you from shutting down correctly.
The source of this problem lies in the fact that when Windows XP shuts down, each running process is given 20 seconds to perform cleanup work by default. If a process does not respond within this timeout period, Windows XP displays this dialog. To solve this problem, you can modify the default timeout by editing the registry. The time-out value is specified by the WaitToKillAppTimeout value under the following registry key:
This value is expressed in milliseconds. You can use Registry Editor to modify this value and then either restart the computer for the change to take effect or restart explorer.exe.