FaceTime registration error - other ideas?

I am still having trouble with this Registration error using FaceTime.

I don't use FaceTime very often, but I have used it successfully in the past.

I first received the error about a month ago (Feb-Mar 2012).

I am using the Apple firewall:

Firewall Settings:

Mode: Limit incoming connections to specific services and applications

Applications:

com.apple.FaceTime: Allow all connections

com.apple.iTunes: Allow all connections

Firewall Logging: No

Stealth Mode: No

The hosts file has no mention of apple.com or verisign.com:

##

# Host Database

#

# localhost is used to configure the loopback interface

# when the system is booting. Do not change this entry.

##

127.0.0.1 localhost

255.255.255.255 broadcasthost

::1 localhost

fe80::1%lo0 localhost

and the date and time are correct via time.apple.com

Any additional thoughts?