Where is your server located? This appears to be a DNS issue on paypal's part. They will probably get it resolved soon.
In the meantime I've updated your paypal include file to use the IP address instead of the domain name for their server and it is working correctly now. However, paypal does update their IP address semi-regularly and without notice, so you should go back to using the domain once it starts working again.
I made the change on line 512 of: /WA_eCart/PP_ECO_Scripts/PP_ECO_PHP.php