need to add "Read more" button to the toolbar of FCKeditor

Hello All,
i need to add a button for "Read more" feature to the toolbar of FCKeditor.
i searched the web & i found a plugin for this button. so added this plugin to FCKeditor by the following 2 steps:
1-add plugin to fckconfig.js
FCKConfig.Plugins.Add( 'drupalbreak') ;

2-add the button to the default toolbar:
FCKConfig.ToolbarSets["Default"] = [
['Source','DocProps','-','Save','NewPage','Preview','-','Templates'],
['Cut','Copy','Paste','PasteText','PasteWord','-','Print','SpellCheck'],
['Undo','Redo','-','Find','Replace','-','SelectAll','RemoveFormat'],
['Form','Checkbox','Radio','TextField','Textarea','Select','Button','ImageButton','HiddenField'],
'/',
['Bold','Italic','Underline','StrikeThrough','-','Subscript','Superscript'],
['OrderedList','UnorderedList','-','Outdent','Indent'],
['JustifyLeft','JustifyCenter','JustifyRight','JustifyFull'],
['Link','Unlink','Anchor'],
['Image','Flash','Table','Rule','Smiley','SpecialChar','PageBreak'],
'/',
['Style','FontFormat','FontName','FontSize'],
['TextColor','BGColor'],
['FitWindow','-','About'],
['DrupalBreak'] //added by Eman
] ;

but when i try to run the editor the following error message appears:
Unknown toolbar item "DrupalBreak"

can any one help me in solving this problem?