cgi_multipart_eof_fix was not loaded

刚开始学习，请教大家
我执行server脚本提示

=> Booting Mongrel (use 'script/server webrick' to force WEBrick)
=> Rails application starting on http://0.0.0.0:3000
=> Call with -d to detach
=> Ctrl-C to shutdown server
** Ruby version is up-to-date; cgi_multipart_eof_fix was not loaded
!!! Path to log file not valid: log/mongrel.log
mongrel::start reported an error. Use mongrel_rails mongrel::start -h to get hel
p.
Exiting

Ruby version is up-to-date; cgi_multipart_eof_fix was not loaded

怎么加载cgi_multipart_eof_fix？

!!! Path to log file not valid: log/mongrel.log

我在该目录下新建mongrel.log也没有用~怎么回事？

问题很弱，谢谢