Installation problem of FCKEditor on MediaWiki

I keep getting this error when I try to edit a page:

Detected bug in an extension! Hook FCKeditor_MediaWiki::onCustomEditor failed to return a value; should return true to continue hook processing or false to abort.

Backtrace:

#0 C:\xampp\htdocs\wiki\includes\Wiki.php(502): wfRunHooks('CustomEditor', Array)
#1 C:\xampp\htdocs\wiki\includes\Wiki.php(63): MediaWiki->performAction(Object(OutputPage), Object(Article), Object(Title), Object(User), Object(WebRequest))
#2 C:\xampp\htdocs\wiki\index.php(116): MediaWiki->initialize(Object(Title), Object(Article), Object(OutputPage), Object(User), Object(WebRequest))
#3 {main}

Retrieved from "http://localhost/wiki/index.php/Main_Page"