Mine

if ((isset($_POST['submit'])==true) && (isset($_POST['checkbox'])==true))   		{ header("location: http://www.fullurl.com/nextpage.php"); }    	else if ((isset($_POST['submit'])==true) && (isset($_POST['checkbox'])==false))  	{ $Error = "You must check the box to continue."; }  ?>  <html>  <head>  <body>  	<form action="test1.php" method="post">   		<? if (isset($Error)==true) { echo $Error; } ?>   		<input type="checkbox" name="checkbox"> You must check this.   		<input type="submit" name="submit">  	</form> </body>