use acts_as_versioned plug-in lead to an unknown exception:

"NoMethodError: You have a nil object when you didn't expect it!"

from /opt/local/lib/ruby/gems/**1**.8/gems/activerecord-**2**.**1**.**0**/lib/active_record/attribute_methods.rb:**211**:in

`version='
from /Users/toby/rorbar/olhc_website/vendor/plugins/**acts_as_versioned**/lib/**acts_as_versioned**.rb:431:in

`send'
from /Users/toby/rorbar/olhc_website/vendor/plugins/**acts_as_versioned**/lib/**acts_as_versioned**.rb:431:in

`set_new_version'

It is maybe because of out-of-day acts_as_versioned plugin with rails 2.1 or above.

The partial updates feature in 2.1 caused a conflict with the the way

acts_as_versioned handles it’s own change history. Check out the latest master on github as this has been resolved: http://github.com/technoweenie/acts_as_versioned/tree/master

see http://www.nabble.com/acts_as_versioned-and-Rails-2.1-td17665890.html

To solve this. reinstall the acts_as_versioned gem. or download tarbal/zip package from GitHub(link above) and unzip into the rails application’s vendor/plugin directory. (i have problem in re-installation. it always install only Docs. even give a -f augment Do anyone know how to re-install a gems plug-in?)

==Chinese version== 使用acts_as_versioned插件時導致了以下的錯誤

"NoMethodError: You have a nil object when you didn't expect it!"

from /opt/local/lib/ruby/gems/**1**.8/gems/activerecord-**2**.**1**.**0**/lib/active_record/attribute_methods.rb:**211**:in

`version='
from /Users/toby/rorbar/olhc_website/vendor/plugins/**acts_as_versioned**/lib/**acts_as_versioned**.rb:431:in

`send'
from /Users/toby/rorbar/olhc_website/vendor/plugins/**acts_as_versioned**/lib/**acts_as_versioned**.rb:431:in

`set_new_version'

這可能是因為您在rails 2.1或更新的版本中使用老舊的acts_as_versioned插件

The partial updates feature in 2.1 caused a conflict with the the way 有一部分rails 2.1的新功能導致acts_as_versioned插件處理歷史紀錄功能壞掉 acts_as_versioned handles it’s own change history. Check out the latest master on github as this has been resolved: 請從github弄出最新的程式碼，master已經修正: http://github.com/technoweenie/acts_as_versioned/tree/master

請參考 http://www.nabble.com/acts_as_versioned-and-Rails-2.1-td17665890.html

要解決這個問題，重新安裝acts_as_versioned插件，或直接從github網站下載tarbal/zip的壓縮檔，解壓縮到rails目錄的vendor/plugin子目錄中

(但是我重新安裝有問題，即使我下了-f參數，他還是只會安裝新的文件工具，有人知道要如何確實重新安裝gems的插件嗎？)