After posting a similar complaint today on the forums I stubmled across this post. I wouldn't be following proper etiquette if I didn't post my findings.
I too was having an issue with EFW 2.4.1 talking to EFW 2.5.1 over IPSEC tunnel using hostname (created by dyndns.org) I have one site that has a static IP and the other which is dynamic. All was well with the respective IP's in the hostname field. When I changd the IP to a hostname I could establish connection. Chcked logs and found INVALID ID INFO.
After finding this post, I changed the LocalID and RemoteID to the hostnames of that particular site. Clicked save, and no more erros. Connection established.
So to your repsonse, your knowledge of VPN inside and out did provide assistance to one lonely IT guy out there who does look at these forums, and to that.. I say THank you!