Undefined variable php error

When I hit my submit button I get an error on the reply page

Notice: Undefined variable: check_msg in E:\clients\ddr emp\mailer.php on line 18

the link: http://dev-rockwood.virtualhorizons.com/about.htm#

click on the download catalog link on the right

Why am I getting this error?


<?php 
if(isset($_POST['submit'])) { 
 
$to = "[EMAIL="dhowe@virtualhorizons.com"]dhowe@virtualhorizons.com[/EMAIL]"; 
$subject = "Request for Catalog"; 
$name_field = $_POST['name']; 
$email_field = $_POST['email']; 
$address_field = $_POST['address'];
$city_field = $_POST['city'];
$state_field = $_POST['state'];
$zip_field = $_POST['zip'];
$phone_field = $_POST['phone'];
$catalog_field = $_POST['catalog'];
$message = $_POST['comments']; 
 
foreach($_POST['check'] as $value) { 
$check_msg .= "Wanting to Purchase: $value
"; 
} 
 
$body = "From: $name_field
 E-Mail: $email_field
 Address: $address_field
 City: $city_field
 State: $state_field
 Zip: $zip_field
 Phone: $phone_field
 Catalog Option: $catalog_field
 $check_msg Message:
 $message
"; 
 
if($catalog_field == "9mb"){ 
 print("Thank You $name_field for requesting our catalog."); 
 
} else if($catalog_field =="1mb") {
 
 print("Thank You $name_field for requesting our catalog."); 
 
}else{
 echo "nothing";
}
mail($to, $subject, $body);   
} else { 
echo "Ahrggg!"; 
} 
?>