这是什么错误阿
帮我看看这是什么错误把     谢谢
D:\netbeansProj\HelloWorld\nbproject\build-impl.xml:157:   Could   not   create   task   or   type   of   type:   nb-prep.
Ant   could   not   find   the   task   or   a   class   this   task   relies   upon.
This   is   common   and   has   a   number   of   causes;   the   usual  
solutions   are   to   read   the   manual   pages   then   download   and
install   needed   JAR   files,   or   fix   the   build   file:  
  -   You   have   misspelt   'nb-prep '.
      Fix:   check   your   spelling.
  -   The   task   needs   an   external   JAR   file   to   execute
          and   this   is   not   found   at   the   right   place   in   the   classpath.
      Fix:   check   the   documentation   for   dependencies.
      Fix:   declare   the   task.
  -   The   task   is   an   Ant   optional   task   and   the   JAR   file   and/or   libraries
          implementing   the   functionality   were   not   found   at   the   time   you
          yourself   built   your   installation   of   Ant   from   the   Ant   sources.
      Fix:   Look   in   the   ANT_HOME/lib   for   the   'ant- '   JAR   corresponding   to   the
          task   and   make   sure   it   contains   more   than   merely   a   META-INF/MANIFEST.MF.
          If   all   it   contains   is   the   manifest,   then   rebuild   Ant   with   the   needed
          libraries   present   in   ${ant.home}/lib/optional/   ,   or   alternatively,
          download   a   pre-built   release   version   from   apache.org
  -   The   build   file   was   written   for   a   later   version   of   Ant
      Fix:   upgrade   to   at   least   the   latest   release   version   of   Ant
  -   The   task   is   not   an   Ant   core   or   optional   task  
          and   needs   to   be   declared   using   <taskdef> .
  -   You   are   attempting   to   use   a   task   defined   using  
        <presetdef>   or   <macrodef>   but   have   spelt   wrong   or   not  
      defined   it   at   the   point   of   use
Remember   that   for   JAR   files   to   be   visible   to   Ant   tasks   implemented
in   ANT_HOME/lib,   the   files   must   be   in   the   same   directory   or   on   the