What PHP version are you running on the machine?
If you are using PHP 5.3.4 or higher, you'd need to change the line to the following instead:
Where you would remove the form=, portion of that line. If that still does not work or you aren't using PHP 5.3.4 or higher, please submit a ticket to WHM > Support Center > Contact cPanel or using the link in my signature. If you could post the ticket number here if you open one, that would be highly appreciated.
url_rewriter.tags = "a=href,area=href,frame=src,input=src,fieldset="