rubyonrails error when update to gem 1.8.1

I update gem to the latest 1.8.1 and now when i use rails command i got errors as below

NOTE: Gem::Specification#default_executable= is deprecated with no replacement. 
It will be removed on or after 2011-10-01.
Gem::Specification#default_executable= called from /Library/Ruby/Gems/1.8/specifications/rubygems-update-1.7.2.gemspec:11.
NOTE: Gem::Specification#default_executable= is deprecated with no replacement. It will be removed on or after 2011-10-01.
Gem::Spec开发者_开发问答ification#default_executable= called from /Users/Haxrat/.gem/ruby/1.8/specifications/RedCloth-4.2.7.gemspec:10.

Gem 1.8 adds lots of deprecation warnings, see http://blog.zenspider.com/2011/05/rubygems-18-is-coming.html

Most noise coming from the specs themselves can be cleaned up very very easily with gem pristine:

gem pristine --all --no-extensions

You could also directly edit the .gemspecs that are noisy and remove the old methods (e.g. in your case, remove line 11 of /Library/Ruby/Gems/1.8/specifications/rubygems-update-1.7.2.gemspec)

These are just deprecation warnings. Lots of stuff in rubygems is deprecated in this version, read http://blog.zenspider.com/2011/05/rubygems-18-is-coming.html for more details.