http://docs.notepad-plus-plus.org/index.php/Plugin_Central#X Install that plugin (open the zip file, copy the XMLTools.dll to C:\Program Files (x86)\Notepad++\plugins and the content of the ext_libs folder to the root folder of the notepad++ installation (should be C:\Program Files (x86)\Notepad++))
NOTE: Windows will nag about needing Administrator rights. Click OK
Open the dlclist.xml with notepad++
There's a menu at the top. Click on "Plugins", then on "XML Tools" and then on "Check XML Syntax now".