Configuration.xml file format storing setting information is broken for some reason.
Delete the broken xml file and boot Configuration Utility.

Configuration.xml file is stored in a below folder.
　Windows XP
　　C:\Documents and Settings\All Users\Application Data\Microsoft\Point Of Service\Configuration\
　Windows７
　　C:\ProgramData\Microsoft\Point Of Service\Configuration\

In order to boot it by user mode in Windows 7, the file is stored in:
C:\Users\[login user name]\AppData\Local\VirtualStore\ProgramData\Microsoft\PointOfService\Configuration

(Move to the administration folder and click "Compatibility Files" displayed on the menu to move the above path.)