Domain Mapping: Domain Name Is Unavailable To Access

I have a client running a site under my PRProsNet.com MU installation. The site is PRPotion.com. It was working until a day or two ago when my client accidentally deleted the DNS records we had set up for her. Now I attempted to recreate what I believe are the correct DNS settings, but I can not get the domain mapping to work correctly for the site.

I've checked and the site itself works fine as a subdomain of prprosnet.com (http://potionpr.prprosnet.com/ works fine). I have set the A record for PRPotion.com to point to the IP address of prprosnet.com. The TTL is a half hour and it's been well over an hour and still no joy: every time I attempt to map the domain, I get the "Domain Name Is Unavailable To Access" warning and can't map the domain. I've also checked the DNS at viewdns.info and it's showing the updated IP address. So it looks like the DNS entry has populated. Moreover, the error page is a Dreamhost error page (which is where the site should be hosted), so it seems to me like the A record has propagated but for some reason I still can't map to it.

Any ideas? I'm at a loss for what to try next.

Thanks,
--eric