blank / -1 error with ajax in step 2 of Slider Template

http://www.acewebsitepro.com/vpscloud-hosting/
After select particular node of cloud hosting in above specified link and proceeding with order now button to next page. In next page after i enter domain name and click on Check Availability i get -1 or blank error in pop up screen. you can check in following link
http://www.acewebsitepro.com/client-portal/whmcsportal/cart.php/?a=add&pid=14