MX datagrid with and override set dataProvider

[mark goldin]

I am trying to come up with the following datagrid definition:
<mx:DataGrid headerHeight="0" rowHeight="28"
 dataProvider="{_someData">
<mx:Script>
<![CDATA[
override public function set dataProvider(value:Object):void
{
if (value)
{
}
else
{
}
}
]]>
</mx:Script>
<mx:columns>
........

I am getting:
Method marked override must override another method.

Any idea why am I getting it?

Thanks