Bitcoinica.com has an invalid DNSSEC configuration and is not reachable for users with DNSSEC validation enabled (this is known for a few weeks
Most ISPs do not validate DNSSEC, but a few do, like Comcast. Comcast set up a temporary exempt to allow DNS resolution for bitcoinica.com despite the DNSSEC validation failure. This exempt will be removed on Tuesday, May 29 (http://www.dnssec.comcast.net/
). Thus, bitcoinica.com will be offline for Comcast users.
Test here if your DNS resolver validates DNSSEC signatures: http://dnssec.vs.uni-due.de
If the result is YES, then you're either a Comcast customer or you already can't reach bitcoinica.com (like "Could not locate remote server").
Solution: Bitcoinica has to login at their registrar and remove the two erroneous DS records (see dnsviz.net
Workaround: add 220.127.116.11 as DNS server in your network configuration (this disables
DNSSEC validation – make sure you want this).