Where is 64 bit containers?

I'm using 1.9 for about two years, I feel thanks to ProxmoxVE.
I have installed the 3.0 to test 64bit containers.

However, I cannot find where is a 64bit CentOS containers.

The target machine is Dual CPU 64bit, Mem 32G.

I downloaded centos-6-x86_64.tar.gz from
http://openvz.org/Download/template/precreated.
And when I upload the file, is the following error.

Error 400: Parameter verification failed.
filename: missing '.iso' extension

I cannot find same problem at the forum.
What's the problem?

Eiji