I'd like to chime in and state that I'm having this very same issue, sans firewall. I'm on my local network with nothing between and getting the same error if I try to connect via https. If I try connecting via http, I can connect, but get a different error that warrants a thread of its own.
The particulars:
Release 5.0.4_GA_2101.RHEL5_64_20080321154100 CentOS5_64 FOSS edition
Mac OS X 10.5.2 - iCal 3.0.2 |