W3 Total Cache and Domain Mapping Purchasing not working

I'm using the Domain Mapping plugin and it works great. I especially love the enom feature to allow my members to purchase domains. The only problem is I'm using W3 Total Cache and it's blocking the page to buy a domain (it just loads a white screen). I confirmed that this is definitely W3 Total Cache that is causing this error by deactivating the plugin and trying without it activated.

The page that loads when you attempt to purchase a domain is admin-ajax.php but with a very long string after it. I know I can configure W3 Total Cache to not cache admin-ajax.php however I'm not familiar with regular expression.

So what regular expression notation do I need to put in order to tell W3 Total Cache not to cache any variation of admin-ajax.php??

Any help would be very much appreciated!

Thanks,
Tim