I can not connect to my friends Minecraft Hamachi server

I am trying to connect to my friends Hamachi server, but whenever I go to my sever selection, it says can not connect. Is there something I am doing wrong? I have been using his server for a while, and this just started happening. I can connect to my other servers, but that one is not working.

Here is his server.properties:

#Minecraft server properties
#Sun Dec 02 12:50:07 EST 2012
generator-settings=
allow-nether=true
level-name=world
enable-query=false
allow-flight=false
server-port=25565
level-type=DEFAULT
enable-rcon=false
level-seed=
server-ip=
max-build-height=256
spawn-npcs=true
white-list=false
spawn-animals=true
snooper-enabled=true
hardcore=true
texture-pack=
online-mode=true
pvp=true
difficulty=1
gamemode=0
max-players=20
spawn-monsters=true
view-distance=10
generate-structures=true
motd=A Minecraft Server

Are you sure you're using the correct Hamachi IP?

On November 19th, all Hamachi IPs everywhere changed. The reason is that the 5.x.x.x IP-space, which Hamachi has always used because it was never in use anywhere else, began to be publicly routed (ie. used).

In a somewhat humorous twist, Hamachi decided to begin using the UK's Ministry of Defense's IP address space, 25.x.x.x, which was also recently in the news for having a block of 4-million IPs they're hoarding to themselves for internal use.

So, in short, all Hamachi IP's now begin with the number 25. Make sure the server you're connecting to does, too. And make sure neither you nor the server are running any software which blocks traffic from those IPs (such as PeerBlock!)

(Also, if the server-ip setting in server.properties is not blank, make sure it to set to the new IP as well. If it is blank, make sure the server has Hamachi set to the default network adapter; see my other answer)

If my other answer does not help, the most common problem with Hamachi is not having it set as the default adapter (this isn't always necessary; it seems to be hit-or-miss with some games).

Here is a guide for doing that in XP/Windows 2k. To do it in Vista/7:

1. Go to start --> control panel --> Network and Internet --> View Network Status and Tasks --> Change Adapter Settings --> (hit 'alt') --> Advanced --> Advanced Settings.
2. Click on "Hamachi," then click the up-arrow until Hamachi is at the top of the list.
3. You may need to restart your computer afterwards. You usually shouldn't have to, but you may also need to undo this setting to use the internet like normal again :)

Make sure Hamachi is set to the default adapter on both the client and the server.

And finally, if none of this works, try using Tunngle instead. I've had much better luck with it than Hamachi in the past; unlike Hamachi, it's specifically designed for games.