The server is currently not on 1.7.2 and you will not be able to connect on it.
To get on the server follow theese steps:
1.Go onto your minecraft browser
2. At the bottom left there is a button that says profiles
3.Click Edit Profile
4.Look at the box that says version selection
5. Click the drop down box and click 1.6.4
6. Select play game

Then if you play on other servers with 1.7.2 then follow the same steps but select 1.7.2 in the drop down box.

Hope this helps xD