POST field is empty

Hello,

I updated my editor from 2.3.2 to 2.4. But after the update the editor doesn't fill the hidden field. When i submit the form with the FCKEditor the hidden field for the editor is empty.

I didn't change anything in de code (i use php):

$oFCKeditor = new FCKeditor('main_content');
$oFCKeditor->BasePath = 'fckeditor/';
$oFCKeditor->Value = $maincontent;
$oFCKeditor->ToolbarSet = "Basic";

Can anybody help me with this problem? I can't find a solution.